Stirling engine having platelet heat exchanging elements

ABSTRACT

The present invention provides heat exchanging elements for use in Stirling engines. According to the present invention, the heat exchanging elements are made from muliple platelets that are stacked and joined together. The use of platelets to make heat exchanging elements permits Stirling engines to run more effiecient because the heat transfer and combustion processes are improved. In one embodiment, multi-stage combustion can be introduced with platlets, along with the flexibility to use different types of fuels. In another embodiment, a single component constructed from platelets can provide the heat transfer rquirements betweeen the combustion gas/working gas, working gas in the regenerator and the working gas/coolant fluid of a Stirling engine. In another embodiment, the platelet heat exchanging element can recieve solar energy to heat the Stirling engine&#39;s working gas. Also, this invention provides a heat exchanging method that allows for multiple fuilds to flow in opposing or same direction.

FIELD OF THE INVENTION

The present invention relates to Stirling engines and more particularlyto heat exchanging elements thereof which are formed of platelets.

BACKGROUND OF INVENTION

The basic concept of the Stirling engine dates back to the developmentsof Robert Stirling in 1817. Over the years, numerous applications forthe Stirling engine have been investigated and evaluated. For example,one potential use of the Stirling engine is in automobiles and the likeas a prime mover. In addition, the Stirling engine may be used as anengine power unit for hybrid electric applications. Other potentialapplications are the use of the Stirling engine as an auxiliary powerunit and the use of the Stirling engine in marine applications and solarenergy conservation applications.

Stirling engines have a reversible thermodynamic cycle and therefore canbe used as a means of delivering mechanical output energy from a sourceof heat, or acting as a heat pump through the application of mechanicalinput energy. Using various heat sources, mechanical energy can bedelivered by the engine. This energy can be used to generate electricityor be directly mechanically coupled to a load.

One of the disadvantages of current Stirling engines is theirinefficiency due to the presence of dead volume of a working gas and theoverall volumetric size of a burner device of the heat exchangingassembly. A heat transfer system utilizes heat transfer from the burnerdevice to the working gas to cause a piston to be displaced as theworking gas expands under heat and then compresses (contracts) uponcooling of the working gas. One conventional burner device is anapparatus in which air and fuel are injected into the burner device andthen ignited to cause heat to be generated. The working gas is carriedwithin a plurality of heater tubes, which are positioned proximate tothe burner device so that heat is transferred from the burner device tothe working gas flowing within the heater tubes.

One end of each heater tube is in communication with a piston chamberwhich houses one or more pistons and the heated, expanded working gascauses displacement of the one or more pistons within the pistoncylinder. The one or more pistons are operatively connected to otherworking mechanical components for moving a drive member, such as acrankshaft, to cause mechanical energy to be delivered by the engine.

Because a single burner device is used to generate and effectuate heattransfer to the working gas flowing within a number of heater tubes,heat is often not evenly distributed to the working gas within theheater tubes. The burner device in conventional devices often has alength of 14 inches or greater for a 3-kilowatt Stirling engine and thelength of each heater tube from the piston cylinder to a point proximateto the burner device is about 6 inches or more. The gas therefore musttravel 6 inches up the heater tube and then 6 inches back down theheater tube to the piston cylinder after it has been heated. Theassociated disadvantage of such a system is that conventional heatertubes usually contain a dead volume of working gas. This refers to thevolume of working gas that has not moved out of the heater tube duringthe expansion/compression combustion process. In other words, thisconstitutes a volume of stagnant working gas. This results ininefficient heat transfer from the burner device to the working gas andin turn leads to inefficient operation of the Stirling engine itself.

In addition, due to the typical size of the burner device, the burnerdevice first heats a significant volume of air before heat transferoccurs to the working gas. This results in a considerable amount ofenergy being consumed before the working gas is heated and as a result,the working gas is exposed to less heat due to the inefficiencies of theburner device. In other words, a lot of the heat produced by the burnerdevice does not get transferred to the working gas.

Accordingly, there is a continuing need to design a more efficient heattransfer manifold for use in a Stirling engine.

SUMMARY OF INVENTION

The present invention is directed to a heat exchange manifold for use ina Stirling engine. According to the present invention, the heat exchangemanifold is provided using a platelet construction. More specifically,the heat exchange manifold is formed of multiple platelets that arestacked and joined together. A platelet device is a device, which isdesigned to control and manage fluid flow and is constructed ofindividual layers (called platelets). The platelet construction of theheat exchange manifold provides integrated fluid management (IFM), whichadvantageously permits the Stirling engine to run more efficient becausethe heat exchange and combustion process are improved.

The platelets have openings and conduits formed therein which areorientated relative to one another to form the elements of the heatexchange manifold. For example, the manifold includes a combustionchamber having fuel and air intake conduits for delivering fuel and airto the combustion chamber and an exhaust conduit for venting exhaustgases and the like from the combustion chamber. The manifold alsoincludes a working gas circuit, which includes one or more working gasconduits, which are formed in the platelet manifold proximate to thecombustion chamber so that heat is transferred from the combustionchamber to the working gas flowing within the working gas conduits.

This platelet construction advantageously permits precision fabricationof the conduits and combustion chamber in the manifold. This results inmore efficient heat transfer to the working gas as the overall size ofeach individual combustion chamber and each working gas circuit issubstantially reduced in comparison with conventional manifolds due tothe design of the present invention. More specifically, instead ofhaving one large burner device with one combustion chamber and 36 or soworking gas circuits (heater tubes) per piston cylinder, the manifold ofthe present invention has a substantially greater number of individualcombustion chambers, e.g., over 100 and preferably over 200 per pistoncylinder, as well as over 100 hundred working gas circuits. As a result,the dimensions of each combustion chamber and each working gas circuitare substantially reduced and may be precisely tailored using platelettechnology. This results in a reduction of dead volume in each workinggas circuit, improved heat transfer from the combustion chamber to theworking gas, and improved efficiency of the combustion process performedin the combustion chamber.

In another aspect of the present invention, platelet technology is usedto incorporate the internal region of the Stirling displacer cylinderhead end into a platelet stack, which provides multiple heat exchangers.In a first aspect, the cylinder head end has working gas channels andports formed therein to permit the working gas to flow to and from thecylinder head end region. By forming the working gas channels in thehead end, an even more effective and efficient heat transfer surfacearea is provided and this results in a more compact and lighter weightStirling engine. In another aspect, the present invention provides anintegrated structure in which all of the major parts of the head end ofthe Stirling cycle engine are integrated into one cylindrical plateletdevice. The use of very small platelet coolant passageways makespossible small, yet highly efficient heat exchangers. In other words andaccording to one embodiment, channeled platelet members are annularlyarranged to form a piston chamber and also provide all of the heatexchangers for the head end.

In yet another aspect of the present invention, a multi-stage combustorfor use in the Stirling engine is provided and may or may not includeinter-stage cooling. The combustors of the present invention are able toreduce the emission of NO_(x) by having a first combustor which operatesat fuel rich or stoiochiometric conditions (low NO_(x) emission) and asecond combustor which introduces secondary air to dilute the combustiongases and reduce the combustion temperature while maintaining the NO_(x)emission at low levels. High system performance is still maintained.

In yet another embodiment, the head end of the Stirling engine includesa working gas heat exchanging plate which is bonded on top of a plateletmanifold which is itself coupled to the head end of the piston cylinder.The platelet manifold includes a number of channels, which receive theworking gas and serve to both distribute the working gas to the heatexchanging plate and also provide communication ports to the pistonchamber, so that the working gas may flow into and out of the pistonchamber. The heat exchanging plate has a number of heat transferpassageways to efficiently heat the working gas and to provide metalcooling capability. The heat exchanging plate is in fluid communicationwith the platelet manifold so that the heated working gas flows into andout of the channels of the manifold. The working gas is heated as itflows through the plate because one surface of the plate is in directcontact with the hot combustion gases formed during the combustionprocess and actually, the plate partially forms the combustion chamber.

A platelet air injector is provided and is a platelet manifold forunburned combustion air and acts to simultaneously cool the air manifoldplatelets and preheat the incoming combustion air. The platelet airinjector has a number of swirler orifices formed therein for injectingair into the hot combustion gases as they flow from the combustionchamber. The air is aimed at an upper surface of the heat exchangingplate to enhance combustion mixing and aid in the heat transfer betweenthe hot combustion gases and the plate. This embodiment utilizesmulti-staged micro-combustion for burning the fuel rich gas tocompletion resulting in many advantages described hereinafter.

Other features and advantages of the present invention will be apparentfrom the following detailed description when read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a heat transfer manifold for use in a Stirlingengine according to one embodiment;

FIG. 2 is top plan view of the heat transfer manifold of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 1;

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 1;

FIG. 5 is a cross-sectional view taken along the line 5-5;

FIG. 6 is a cross-sectional view taken along the rectangle 6 shown inFIG. 1;

FIG. 7 is a cross-sectional view taken along the line 7-7 of FIG. 1;

FIG. 8 is a schematic of a heat transfer manifold for use in a Stirlingengine according to another embodiment;

FIG. 9 is a top plan view of the heat transfer manifold of FIG. 8;

FIG. 10 is a cross-sectional view taken along the line 10-10 of FIG. 8;

FIG. 11 is a cross-sectional view taken along the line 11-11 of FIG. 8;

FIG. 12 is a cross-sectional view taken along the line 12-12 of FIG. 8;

FIG. 13 is a cross-sectional view taken along the line 13-13 of FIG. 8;

FIG. 14 is a cross-sectional view taken along the line 14-14 of FIG. 8;

FIG. 15 is a cross-sectional view taken along the rectangle 15 shown inFIG. 8;

FIG. 16 is a cross-sectional schematic view of a heat exchange memberincorporating a displacer cylinder head end of a Stirling engine;

FIG. 17 is a simplified top plan view of channeled platelet heatexchangers, which incorporates the piston cylinder and head end of theStirling engine and is inserted into a housing;

FIG. 18 is a cross-sectional view taken along the line 18-18 of FIG. 17;

FIG. 19 is a fragmentary top plan view of the channeled heat exchangersof FIG. 17 shown in an extended, unwound position;

FIG. 20A is a cross-sectional view taken along the line 20-20 of FIG.16;

FIG. 20B is a cross-sectional view of a first region of the structure ofFIG. 16;

FIG. 21A is a cross-sectional view taken along the line 21-21 of FIG.16;

FIG. 21B is a cross-sectional view of a first region of the structure ofFIG. 16;

FIG. 22A is a cross-sectional view taken along the line 22-22 of FIG.16;

FIG. 22B is a cross-sectional view of a first region of the structure ofFIG. 16;

FIG. 23 illustrates different channel structures of the heat exchangesections in the heat transfer platelet use in a Stirling engineaccording to one embodiment;

FIG. 24 is a schematic of a multi-stage combustor for use in a Stirlingengine according to one embodiment;

FIG. 25 is a graph illustrating NO and CO emission levels versus air toNG flow rate concerning the operation and advantages of the multi-stagecombustor of FIG. 24;

FIG. 26 is a schematic of a multi-stage combustor for use in a Stirlingengine according to another embodiment.

FIG. 27 is a cross-sectional view of a working gas heat exchangerincorporated with a combustion device and the hot end of a Stirlingengine;

FIG. 28 is a bottom plan view of an exemplary working gas heat exchangeplatelet;

FIG. 29 is an enlarged partial top plan view of an air injector plateletfor use with the device of FIG. 27;

FIG. 30 is a cross-sectional view of a working gas heat exchangerillustrating a hot end having a solar focusing unit for providing energyto the working energy;

FIG. 31 is a bottom plan view of another exemplary working gas heatexchange platelet;

FIG. 32 is a top plan view of a bi-directional fluid transfer duct foruse in a hot end of the Stirling engines of the prior embodiments;

FIG. 33 is a perspective view of the bi-directional fluid transfer ductof FIG. 32 showing inlet and outlet ports formed therein for directingthe fluid with discrete flow circuit flow paths;

FIG. 34 is a top plan view of an end plate for use with thebi-directional fluid transfer duct of FIG. 32 to provide fluid inletsand/or outlets into and out of the discrete flow circuit flow paths;

FIG. 35 is a partially exploded perspective view illustrating anexemplary heat exchanger; and

FIG. 36 is an enlarged partial view of a section of the heat exchangerof FIG. 35 illustrating a method of attaching end plates to the heatexchanger body.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1-7, a heat transfer manifold for use in a Stirlingengine is shown and indicated at 10. It will be appreciated and will bedescribed in greater detail hereinafter, that the heat transfer manifold10 is intended to be used with conventional type Stirling engines andthe heat transfer manifold 10 is designed to replace the existing “hotend” of the Stirling engine. The term “hot end” is used herein to referto the end of the Stirling engine which includes a heat transfer system.As previously mentioned, the hot end of a conventional Stirling enginegenerally includes an air inlet, a fuel inlet, exhaust means, a fuel/airmixing chamber, a burner device (combustion chamber) and a number ofheater tubes, which carry the working gas, spaced around the burnerdevice. Combustion of the fuel/air mixture within the burner devicecauses heating and expansion of the working gas. The working gas flowsinto and out of a piston cylinder which houses a displacer pistonoperatively connected to a working piston. As the gas expands, thedisplacer piston and working piston are displaced within the pistonchamber.

According to the present invention, the heat transfer manifold 10 isdesigned to replace the burner device, heating tubes, and other relatedcomponents of the heat transfer system of a conventional Stirlingengine. The heat transfer manifold 10 shown in FIGS. 1-7 is preferablyused in combination with one piston assembly, generally indicated at100. The piston assembly 100 includes a piston cylinder 110, whichhouses a displacer piston 120 and a working piston, partially shown at130. The displacer piston 120 is operatively connected to the workingpiston 130. Generally, the piston assembly 100 has an annular shape withthe piston cylinder 110 being an annular cavity in which the displacerpiston 120 and working piston 130 move in an axial direction therein.The end of the piston assembly 100 which faces and seats against theheat transfer manifold 10 typically has a heater head member 111. Asshown in FIG. 1, the exemplary heater head member 111 partially enclosesthe piston cylinder 110 and also forms a flange 113, which extendsoutwardly from a wall of the piston cylinder 110. The flange 113 servesas a support surface for the heat transfer manifold 10. According to oneaspect of the present invention and as will be described in greaterdetail hereinafter, the heater head member 111 has a number of openings115 formed there through for providing fluid communication between thepiston cylinder 110 and the heat transfer manifold 10.

Broadly, the heat transfer manifold 10 generates and transfers heat to aworking gas which is in fluid communication with the piston cylinder 110so that the expansion of the working gas within the piston cylinder 110causes the displacer piston 120 and the working piston 130 to move inthe axial direction away from the heat transfer manifold 10.

According to the present invention, the heat transfer manifold 10 isformed of a stack of platelets, generally indicated at 200, that havebeen joined together in any one of a variety of ways, such as diffusionbonding or brazing. Platelets are thin sheets of metal, metal alloys,ceramics, etc., which are joined to form a monolithic structure. Theprecise thickness of the platelet is not critical and typically, eachplatelet has an approximate thickness between 0.001 inch to about 0.040inch.

The exemplary heat transfer manifold 10 includes an air inlet 40 whichcommunicates with the surrounding environment outside of the heattransfer manifold 10 or may be connected to a supply of air or other gaswhich can be used to combust or catalyze the combustion of the fuel. Asbest shown in FIGS. 1, 2, and 6, the air inlet 40 is defined by anopening 42 formed in an air/fuel platelet zone 210, which comprises aplurality of platelets at one end of the heat transfer manifold 10. Itwill be understood that the plurality of platelets are stacked togethersuch that like features are aligned. The air inlet 40 and moreparticularly, the opening 42 thereof is fluidly linked to apredetermined number of discrete combustion chambers 50 by a number ofair intake conduits 60 which are formed in one platelet zone of theplatelet construction 200. Preferably, the air intake conduits 60 arelongitudinal conduits, which are formed in the air/fuel platelet zone210 using suitable and known platelet technology. For example, thedimensions of the air intake conduits 60 may be concisely tailored tothe precise application and may be formed so that dimensions of the airintake conduits 60 are substantially less than conventional air intaketubing and the like. Such precision in forming the air intake conduits60 is possible because photo-etching technology permits the formation ofair intake conduits 60 having reduced dimensions. It will be appreciatedthat the formation of the air intake conduits 60 and other structuresmentioned hereinafter is not limited to using a photo etching processbut rather other suitable techniques may be used, such as laser cutting,etc. A suitable description of a method of chemical etching is disclosedin U.S. Pat. No. 3,413,704, which is incorporated herein by reference.

The manufacture of platelet members is also described in U.S. Pat. Nos.5,387,398; 5,455,401; 5,614,093; 5,683,828; 6,051,331; 5,858,507;5,804,066; and 5,863,671, all of which are herein incorporated byreference.

As best shown in FIGS. 1 and 6, each combustion chamber 50 is in fluidcommunication with one of the longitudinal air intake conduits 60 bymeans of a second air intake conduit 62, which is preferably formed inmultiple platelet zones of the platelet construction 200. One exemplaryplatelet construction 200 includes a plurality of stacked plateletsincluding the air/fuel platelet zone 210, an air pretreat platelet zone220, an air/fuel mixing platelet zone 230, and one more combustionplatelet zones, generally indicated at 240, and an expansion/compressionplatelet zone 250. It will be understood that each platelet zone isactually formed of a number of stacked platelets. The second air intakeconduit 62 is a vertical conduit which is preferably formed in theplatelet zones 210, 220, 230 and includes a first end in fluidcommunication with one of the air intake conduits 60 and a second endwhich is in fluid communication with an air/fuel conduit 70.

Similarly, the heat transfer manifold 10 includes a fuel intake 80having an opening 82 which is in fluid communication with the outside ofthe heat transfer manifold 10 to permit fuel to be delivered to thecombustion device 50 through the opening 82. The opening 82 is formed inthe air/fuel intake platelet zone 210 and is preferably spaced apartfrom the opening 42 of the air intake 40. The fuel intake 80 also has anumber of fuel intake conduits 84 which are preferably formed in onelayer of the platelet construction 200. Preferably, the fuel intakeconduits 84 are longitudinal conduits which are formed in the air/fuelplatelet zone 210. The fuel intake conduits 84 are formed within theplatelet zone 210 at a different level than the air intake conduits 62so that the fuel intake conduits 84 and the air intake conduits 62 donot cross-over and interfere with one another.

The fuel intake 80 also includes a second air intake conduit 86 which isa vertical conduit formed in the platelet zones 210, 220, 230 andincludes a first end in fluid communication with one of the fuel intakeconduits 84 and a second end which is in fluid communication with theair/fuel conduit 70. Thus, both air and fuel are delivered to theair/fuel conduit 70 which preferably comprises a longitudinal conduitformed in the air/fuel mixing platelet zone 230. An air/fuel inletconduit 88 connects the air/fuel conduit 70 to one combustion chamber50. In other words, the air/fuel inlet conduit 88 opens into thecombustion chamber 50 for delivering the air/fuel mixture into thecombustion chamber 50. In the illustrated embodiment, the air/fuel inletconduit 88 is generally perpendicular to the air/fuel conduit 70 andgenerally parallel to the fuel intake conduit 84. It will be understoodthat all of the conduits forming the fuel intake 80 are preferablyformed in the platelets using the above-mentioned formation techniques,e.g., photo-etching, laser cutting, etc.

As used herein, the term “fuel” refers to a material that is combustedto release heat energy. Any number of fuels may be used so long as theyare suitable for use in the environments described herein. In otherwords, the fuel must be combustible under the conditions describedherein and must generate sufficient heat energy to efficiently heat theworking gas. The fuel may come in different forms and may for example bea liquid, solid or gas. One preferred fuel is natural gas, which ismixed with air in a predetermined ratio for the combustion of thismixture. Another fuel that is suitable for use is propane gas (or othertypes of carbon based gases) and yet another suitable fuel is dieselfuel. It will be understood that the above-listed fuels are merelyexemplary and any number of other types of fuels may be used. Whendifferent fuels are used, the hot end may have to be slightly modifiedto permit proper introduction of the fuel into the combustion chamber50. However, the versatility of platelets permits modifications to beeasily made and also these new constructions can be made in stockplatelets so as to tailor the construction for the given application.These slight modifications do not change the overriding physicalprinciples as to how the Stirling engine of platelet constructionoperates.

Because a combustion reaction takes place in the combustion chamber 50,the heat transfer manifold 10 has an exhaust means incorporated into theplatelet structure 200 for venting exhaust gases and the like. Anexhaust port 90 is formed in the air/fuel intake platelet zone 210 andis open to the environment surrounding the heat transfer manifold 10.Similar to the openings 42 and 82, the exhaust port 90 is spaced apartfrom the openings 42, 82 and has an annular shape. A plurality of firstexhaust conduits 92 are formed in one layer of the platelet construction200. Preferably, the first exhaust conduits 92 are longitudinalconduits, which are formed in the air/fuel platelet zone 210. The firstexhaust conduits 92 are formed within the platelet zone 210 at adifferent level than the air intake conduits 62 and the fuel intakeconduits 84 so that the first exhaust conduits 92 do not cross-over andinterfere with the other conduits formed in the platelet zone 210.

A second exhaust conduit 94 is provided in the form of a verticalconduit which is formed in the platelet zones 210, 220, 230, 240 andincludes a first end in fluid communication with one of the firstexhaust conduits 92 and a second end which is in fluid communicationwith an exhaust outlet conduit 96 which is itself in fluid communicationwith the combustion chamber 50. The second exhaust conduit 94 is thusformed in one or more platelets of the combustion platelet zone 240. Inthe exemplary embodiment, combustion platelet zone 240 is actuallyformed of four platelet zones 242, 244, 246, 248 with the exhaust outletconduit 96 being partially formed in the bottommost combustion plateletzone 248. As the fuel burns within the combustion chamber 50, exhaustgas is produced and the exhaust system of the present invention providesa means for venting the exhaust gas from the combustion chamber 50.Exhaust gas from individual combustion chambers 50 is vented through therespective second exhaust conduit 94 into one of the first exhaustconduits 92 and then to the exhaust port 90 for venting to thesurrounding environment.

It will be appreciated that the above-described exhaust system is merelyexemplary in nature and the exhaust outlet conduit 96 may be formed in anumber of different locations. For example, the exhaust outlet conduit96 may communicate with the combustion chamber 50 at an upper section 52thereof instead of a lower section 54 thereof, as shown in FIG. 6.

The combustion chamber 50 is thus designed to receive the fuel and airmixture which is then ignited using any number of suitable ignitiondevices 98 resulting in heat being generated as the fuel burns. Forexample, suitable ignition devices 98 include but are not limited tospark generating devices, electrostatic devices, and any number of otherdevices, which act to cause the selective ignition of the fuel in thecombustion chamber 50. The ignition device 98 may communicate with thecombustion chamber 50 in a number of different ways and for purposes ofillustration only, FIG. 6 shows the ignition device 98 extendinglongitudinally through one of the combustion platelet zones 240 and intothe combustion chamber So. It will be understood that the ignitiondevice 98 may be formed vertically within the heat transfer manifold 10so that the ignition device 98 extends through platelet zones 210, 220,230, 240 and communicates with the upper section 52 of the combustionchamber 50.

Like the conduit elements of the heat transfer manifold 10, thecombustion chamber 50 is formed in various platelets of the plateletconstruction 200 using traditional techniques, e.g., photo-etching.Platelet technology permits the combustion chamber 50 to be moreprecisely dimensioned and shaped for individual applications. Unlike inconventional Stirling engine designs, the heat transfer manifold 10 ofthe present invention has a multitude of combustion chambers 50 insteadof just a single burner device. For example, in one embodiment, for eachpiston cylinder 110, there are over 200 combustion chambers 50 forcausing the axial displacement of the displacer and working pistons 120,130, and more particularly, in one embodiment, there are approximately260 combustion chambers 50 per each piston cylinder 110.

The exemplary combustion chamber 50, shown in FIG. 15, is a generallyannular member and includes the upper section 52 and the lower section54 with the upper section 52 having a greater diameter than the lowersection 54. As best shown in FIG. 6, the lower section 54 has an inwardtaper defined by an inwardly tapered wall 56. This results in thediameter of the lower section 54 being less than the diameter at the topsection 52.

As can be seen in FIG. 5 and in accordance with one embodiment, thecombustion chambers 50 are formed in the heat transfer manifold 10 in aradial relationship so that a number of rings are formed. Unlikeconventional burning devices, which typically have a length greater thanabout 14 inches, the combustion chamber 50 of the present invention hassubstantially reduced dimensions relative to conventional burnerdevices. According to the present invention, the combustion chamber 50has a substantially reduced size relative to the conventional burningdevices. For example, the height of the combustion chamber 50 ispreferably only several inches, about 2 inches, for a 3-kilowatt engine.It will be appreciated that as the size of the Stirling engineincreases, the size of the combustion chamber 50 will also change and inthis case will increase correspondingly.

The heat transfer manifold 10 also includes working gas conduits 300which carry the working gas, which is heated to cause the displacementof the pistons 120, 130 within the piston cylinder 110. Any number oftypes of working gases, which are suitable for use in Stirling engines,may be used in the present invention, including but not limited tohelium gas. Each of the working gas conduits 300 is generally anU-shaped conduit formed in several platelets. In one embodiment, eachworking gas conduit 300 has a pair of open ends 302 which are in fluidcommunication with the piston cylinder 110 to permit the working gas tofreely flow from the piston cylinder 110 and into any number of workinggas conduits 300. An U-shaped bend 301 of the working gas conduit 300 islocated proximate to one or more combustion chambers 50. In theembodiment shown in FIG. 6, the tapered second section 54 of thecombustion chamber 50 is formed between adjacent working gas conduits300. Because of the precision of platelet technology, the working gasconduits 300 can be formed relatively close to the combustion chamber50. This results in more efficient heat transfer from the combustionchamber 50 to the working gas flowing within the working gas conduits300 disposed around the combustion chamber 50. Advantageously, theplatelet construction 200 permits the dimensions of the working gasconduits 300 to be reduced. For example, in conventional heater tubes,the working gas flows within the tube about 6 inches, to a locationproximate the burner device before flowing back 6 inches to the pistoncylinder. In the present invention, the working gas only flows aboutseveral inches within the working gas conduit before flowing back thesame or similar distance to the piston cylinder 110. Because the lengthof the flow path of the working gas is substantially reduced, the amountof dead volume within the working gas conduit 300 is reduced. Thisresults in more efficient flow of the working gas and as a result, theheat transfer efficiency is increased.

One will also appreciate that by providing a substantial number ofcombustion chambers 50 and working gas conduits 300 formed in theplatelet structure 200, the deficiencies which were associated with thedead volume of the conventional burner design are eliminated or at leastsubstantially reduced. Because the volume of the combustion chamber 50is substantially less than the volume of a single burner device, thecombustion is more efficient as less air is required to be heated foreffective heat transfer through the platelet structure 200 to theworking gas. This results in a cleaner combustion process and moreefficient heating of the working gas. For a 3-kilowatt Stirling engine,the heat transfer manifold 10 may have a height between about 4 to about6 inches. In any event, the height of heat transfer manifold 10 isconsiderably less than the height of conventional burner devices. Itwill be appreciated that as the size of the Stirling engine increases ordecreases, the size of the heat transfer manifold 10 will alsocorrespondingly increase or decrease.

As the working gas flowing within the working gas conduits 300 heats, itbegins to expand. Because the ends 302 of the working gas conduits 300are open and fluidly communicate with the piston cylinder 110, theexpanding gas flows within the piston cylinder 110. The working gasserves as a working fluid, which causes the displacement of thedisplacer piston 120 and the working piston 130 within the pistoncylinder 110.

In order for there to be no leaks between the heat transfer manifold 10and the piston assembly 100, the platelet structure 200 is coupled tothe piston assembly 100 such that a seal preferably resultstherebetween. It being understood that the open ends of the working gasconduits 300 are not sealed relative to the piston assembly 100 butrather are in direct fluid communication with the piston cylinder 110 byaligning the working gas conduits 300 with the channels 115. Thus, thenumber of and arrangement of channels 115 within the heater head member111 corresponds to the number of and arrangement of working gas conduits300. A seal between the heat transfer manifold 10 and the pistonassembly 100, more particularly, the heater head member 111, may beformed using conventional techniques so long as the working gas conduits300 and the channels 115 align with one another.

One of skill in the art will also appreciate that the Stirling enginehas a “cold end” which is designed to provide among other things acooling mechanism for cooling the heated working gas. While the heattransfer manifold 10 of the present invention is designed to serve asthe “hot end” of the Stirling engine, the “cold end” may include anynumber of suitable cooling devices, which are designed for use as suchin a Stirling engine. The cooling mechanism effectively withdraws heatfrom the working gas and thus causes compression of the working gas.While some of the energy of the working gas is used to displace thepistons 120, 130, there is still additional energy, which is to bewithdrawn to cause the pistons 120, 130 to retract in the pistoncylinder 110. The cooling mechanism is designed to withdraw this energy(heat) from the working gas.

The “cold end” of the Stirling engine also includes mechanical andelectrical components, which operatively connect the piston assembly 100to the drive portions of the Stirling engine. For example, one or morepiston rods (not shown) typically extend through to the displacer andworking pistons 120, 130 and are operatively connected to one or moreconnector rods (not shown). The one or more connector rods are disposedpartially within the piston assembly 100 and also within a crank case(housing) which is connected to the piston assembly 100. The one or moreconnector rods are mechanically coupled to a crankshaft (not shown),which serves as a drive member. For example, the drive shaft may beconnected to a generator (not shown).

The general details of the operation of a Stirling engine, including the“cold end” thereof, are described in U.S. Pat. Nos. 5,638,684;4,481,771; 5,388,409; and 5,722,239, all of which are incorporatedherein be reference.

The platelet structure 200 is formed by diffusion bonding, brazing, orother type of process. Diffusion bonding involves hot-pressing theplatelets 200 together at elevated temperatures. The diffusion bondingcauses grain growth between the platelets forming structure 200, therebygenerating a monolithic structure with properties of the parentmaterial. The platelets of structure 200 are formed of any number ofsuitable materials and preferably, the platelets are thin sheets ofmetal or metal alloys, such as copper, stainless steel, aluminum,nickel, titanium, and niobium. In addition, the platelets may be formedfrom ceramic materials.

Other details of suitable platelet materials and manufacturing detailsare disclosed in the previously incorporated U.S. Pat. Nos. 5,387,398;5,455,401; 5,614,093; 5,683,828; 6,051,331; 5,858,507; 5,804,066; and5,863,671.

While each of the platelets may have the same or similar width, it willbe appreciated that the platelets do not need to have a generallyuniform width and any one of the platelets may have a width greater orless than the width of the other platelets. In one exemplary embodiment,each platelet has a thickness of approximately 0.020 inch. The plateletsare also not limited to an annular shape but rather may have any numberof shapes, including rectangular or oval shapes. However, it will beunderstood that the platelet may have other thickness depending upon theprecise construction and application.

It will also be understood that the present invention is not limited tothe arrangement of working gas conduits 300 and combustion chambers 50shown in FIGS. 2-5. These arrangements are merely exemplary in natureand illustrate one embodiment of the present invention.

Referring now to FIGS. 8-15, a heat transfer manifold according to asecond embodiment is shown and indicated at 400. The heat transfermanifold 400 is similar to the heat transfer manifold 10 and thereforelike elements are numbered alike.

The heat transfer manifold 400 includes a platelet structure 410 definedby the air/fuel intake platelet zone 210, the air preheat platelet zone220, the air/fuel mixing platelet zone 230, the combustion platelet zone240, and the working gas expansion/compression platelet zone 250. Inthis embodiment, the combustion platelet zone 240 is actually formed byfirst, second, third, and fourth combustion platelet zones 242, 244,246, 248, respectively. In addition, the working gasexpansion/compression platelet zone 250 is defined by first, second,third, and fourth platelet zones 252, 254, 256, and 258.

Like the platelet structure 200, the stack of platelets 410 are joinedtogether to form a single monolithic structure. The stack of platelets410 has a shape which is generally complementary to the shape of thepiston cylinder 110 and accordingly, in this one embodiment, the stackof platelets 410 has a generally annular shape. The manifold 400includes the air intake 40, the fuel intake 80, and the exhaust system90, 92, 94, 96.

In this second embodiment, the combustion chamber 50 is modified so thata series of combustion chambers 50 formed in the manifold 400 areconnected to one another by a combustion connector conduit 420. Thecombustion connector conduit 420 is preferably in the form of alongitudinal conduit formed in one of the platelets of the combustionplatelet zone 240. For example, the combustion connector conduit 420 maybe formed in the third combustion platelet zone 246. As best shown inFIG. 8, the combustion connector conduit 420 has opposing closed ends422 with the conduit 420 communicating with a number of combustionchambers 50 therebetween. For example, each lower section 54 of onecombustion chamber 50 opens into a portion of the combustion connectorconduit 420 to permit heat generated within the combustion chamber 50 tobe transferred to the combustion connector conduit 420. The combustionconnector conduit 420 permits heat to be distributed over a greater areaof the platelet structure 400 so that heat is effectively andefficiently transferred to the working gas flowing within working gasconduits 500.

In the second embodiment, each working gas conduit 500 is defined by aseries of branched tortuous pathways in which the working gas enters theconduit 500 through an inlet 510 and exits the conduit through an outlet520. The flow of the working gas is generally indicated by thedirectional arrow 522. The conduit 500 has a number of U-shaped bends524 which partially define the tortuous flow path of the working gas.The U-shaped bends 524 are formed in the combustion platelet zone 240(e.g., the fourth combustion platelet zone 246). By positioning amultitude of U-shaped bends 524 near the combustion chambers 50 and thecombustion connector conduit 420, the working gas flowing within theseU-shaped bends 524 is more effectively heated by the heat generated inthe combustion chambers 50 and present in the combustion connectorconduit 420. In other words, by branching the conduit 500 into a numberof pathways with portions (U-shaped bends 524) disposed in closeproximity to one combustion chamber 50 and the conduit 420, the volumeof gas exposed to the heat is increased, leading to more efficientheating thereof. After the working gas has been heated, the gas flowsthrough the outlet 520 and into the piston cylinder 110 for displacementof the displacer piston 120.

As shown in FIG. 8, the working gas conduits 500 may have a number ofconnecting conduits 523 which permit inlet/outlet conduits 510 to feedworking gas to a plurality of working gas conduits 500 which arepositioned proximate to a plurality of combustion chambers 50. A numberof inlet/outlet conduits 510 also provided the path for the working gasto enter and exit the piston cylinder 110.

The manifold 400 also includes an ignition device 530, which causes thefuel to selectively ignite resulting in the generation of heat. In oneexemplary embodiment, the ignition device 530 has a first end 532, whichextends beyond a top surface of the platelet zone 210 and an opposingsecond end 534, which is positioned within the combustion connectorconduit 420. The ignition device 530 is formed in the platelet structure410 from the outermost platelet 210 to the platelet having thecombustion connector conduit 420 formed therein, e.g., third combustionplatelet zone 246. Upon actuation of the ignition device 530, the secondend 534 ignites the fuel/air mixture using known techniques, such asgenerating a spark or the like. The actuation of the ignition device 530thus causes the ignition of the fuel/air mixture present in thecombustion chambers 50 and the combustion connector conduit 420.

FIG. 9 shows a top plan view of the manifold 400 of the secondembodiment. FIGS. 10-15 show various cross-sectional views of themanifold 400.

Accordingly, the present invention teaches in one aspect the replacementof the traditional “hot end” assembly of the Stirling engine with a heattransfer manifold 10 formed of a stack of platelets. As one of skill inthe platelet technology understands, each platelet is crafted so thatupon stacking and joining the platelets together, openings and conduitsformed therein are properly orientated to form a single monolithicstructure, which functions as a heat transfer manifold 10.

Advantageously, the use of platelet technology permits the heat transfermanifold 10 of the present invention to be formed of a series ofinterrelated integrated fluid management (IFM) platelets. Byincorporating the present heat transfer manifold 10 into the Stirlingengine, improvements are seen in the combustion process and the overallefficiency of the engine because of improved heat transfer.

Referring to FIG. 16, a hot end of a Stirling engine is generallyindicated at 599 and includes a heat transfer platelet member 600. Aswith other Stirling engine designs, the present invention includes adisplacer piston 610 and a working piston 620. The displacer piston 610and the working piston 620 are operatively connected to one anotherusing conventional methods, including providing a crank 612 connectingthe pistons 610, 620. The crank 612 is typically operatively connectedwith or forms a part of a flywheel assembly (not shown). In addition, aStirling engine typically has a generator (not shown), which isoperatively connected to the crank 612. As one of skill in the artunderstands, a working gas is provided in a Stirling engine and thethermal heating and cooling of this working gas causes movement of thedisplacer piston 610 and the working piston 620. The displacer piston610 actually serves to move or shuttle the working gas around theworking areas of the Stirling engine. Because of the interconnectionbetween the displacer piston 610, the crank 612, the working piston 620and the flywheel and the generator, the movement of one componenttranslates into movement of the other components. More specifically andas will be described in greater detail hereinafter, movement of thedisplacer piston 610 causes energy to be supplied to the flywheel andthe generator in addition to the working piston 620.

In this embodiment, a piston chamber 630 is defined by the plateletmember 600 itself. The piston chamber 630 has a first end 632 and asecond end (not shown) with the displacer piston 610 being disposed nearthe first end 632 and the working piston 620 being disposed between thedisplacer piston 610 and the second end.

According to the present invention, the platelet member 600 incorporatesboth the hot end and the cold end of the heat exchanging components ofthe Stirling engine and also incorporates the displacer cylinder headend into its design. The platelet member 600 is formed using platelettechnology and more specifically, it is formed of a stack of plateletsthat have been joined together in any of a variety of ways, such asdiffusion bonding and brazing. As previously-mentioned, platelets arethin sheets of metal, metal alloys, ceramics, etc., which are joined toform a monolithic structure. The precise thickness of the platelet isnot critical and typically, each platelet has a thickness between about0.001 inch to about 0.040 inch.

In this embodiment, the platelet member 600 includes a number ofchanneled platelet heat exchanger elements, which are inserted into ahousing 640. The housing 640 in one embodiment resembles a pressurevessel surrounding the platelet member 600 and is preferably, a highpressure capable conventionally machined metal housing 640. Typically,the housing 640 has a generally annular shape. The housing 640 has oneor more coolant inlets 642 and one or more coolant outlets 644 formed ina side thereof. In addition, the housing 640 has one or more combustiongas outlets 646 formed in a side thereof. The housing 640 has a firstend 670 and an opposing second end 672. The first end 670 is generallyassociated with the hot end of the platelet member 600 and the secondend 672 is generally associated with the cold end of the platelet member600.

The first end 670 is essentially closed with an end wall 674, which isintegral with an annular sidewall 676 of the housing 640. The wall 674does have a number of openings or ports formed and more specifically,the wall 674 has a plurality of air inlets 678 and a plurality of fuelinlets 680 formed therein. Preferably, the number of inlets 678, 680 andthe dimensions of each are configured so that a mixture of 40% air and60% fuel is introduced into a combustion chamber 689.

Referring now to FIGS. 16-19, the platelet member 600 preferably isformed of channeled heat exchanging elements, which are each generallyindicated at 690 in FIGS. 17 and 19. As best shown in FIG. 19, eachchanneled heat exchanging element 690 is formed of a stack of platelets.The platelet layers shown in FIG. 19 are for purposes of illustrationonly and it will be appreciated that each platelet element 690preferably includes a number of stacked platelets much greater than thenumber of stacked platelets shown in FIG. 19. Each platelet element 690has a generally trapezoidal cross-sectional shape including opposingside faces 691 along with an inner face 693 and an outer face 695. Theinner face 693 has a smaller surface area than the outer face 695.

FIG. 19 shows the channeled platelet elements 690 in an elongatedposition. Because of the corrugated nature of the elements 690, theelements 690 may be manipulated so as to form an annular member as shownin FIG. 17. In the exemplary embodiment shown, the corrugated structurecontains sixteen (16) individual elements 690. When the elements 690 aremanipulated to form the annular structure, side faces 691 of theelements 690 engage one another so that no gaps are present between theside faces 691 of the elements 690. The inner faces 693 form an innerannular surface, generally indicated at 699, and the outer faces 695form an outer annular surface, generally indicated at 701. Preferably,the inner annular surface 699 is a smooth surface and in fact, the innerannular surface 699 defines the piston chamber 630. FIG. 18 is across-sectional view taken along the line 18-18 of FIG. 17, showingopposing platelet elements 690 and also shows that each individualelement 690 is formed of a plurality of platelets.

FIG. 17 also shows that the channeled platelet elements 690 are disposedwithin the housing 640 such that the outer annular surface 701 seatsagainst an inner surface 641 of the housing 640. For purpose ofillustration only and not limitation, an angle A formed defined byconverging planes that contain the side faces 691 is about 22.5°. Itwill be understood that this angle is merely exemplary and dependingupon the number and size of each of the elements 690, the angle willvary. The number of individual platelet elements 690 which form theoverall corrugated shape of the channeled platelet structure will dependupon a number of factors, including the dimensions of each individualplatelet element 690 and the diameter of the housing 640 along with thedesired diameter of the piston chamber 630 which is actually defined bythe channeled platelet elements 690.

The platelet elements 690 each have a first end 702 and an opposingsecond end 704 and are elongated structures which extend from or nearthe second end 672 of the housing 640 to or near the first end 670 ofthe housing 640. As best shown in FIG. 16, there is preferably a space710 between the first end 702 of the elements 690 and the end wall 674of the housing 640. The combustion chamber 689 is defined by acombustion member 720. The combustion member 720 is preferably anannular member having the combustion chamber 689 formed in a centralportion thereof. The combustion chamber 689 is thus an annular spacewhere combustion of air and fuel occurs resulting in heat beinggenerated. In one embodiment, the combustion member 720 is connected tothe end wall 674 and thus forms a part of the housing 640. In thisembodiment, there are a plurality of radial openings, generallyindicated at 722, which define fluid passageways for gas to flow fromthe combustion chamber 689 to the first ends 702 of the plateletelements 690.

It is within the scope of the present invention, that the combustionmember 720 may be formed so that it is a part of the platelet member600. In this instance, the combustion chamber 689 is formed within thecombustion member 720 using platelet technology. In yet anotherembodiment, the combustion member 720 may be formed of platelets but bea separate member from the channeled platelet elements 690. In thisembodiment, the combustion member 720 is coupled to the plateletelements 690 using any suitable technique, including platelet diffusionbonding techniques. In this embodiment, the radial openings 722 areeliminated and instead, an annular space is formed between the first endof the combustion member 689 and the end wall 674.

Preferably, an annular baffle 730 is connected to and extends from theend wall 674 of the housing 640 into the combustion chamber 689. Theannular baffle 730 has an end 732 which is spaced from a lower region734 of the combustion chamber 689. The annular baffle 730 thuspartitions the combustion chamber 689 into a first section 738 and asecond section 740 with the first section 738 being located within theannular baffle 730 and the second section 740 being located between theannular baffle 730 and the combustion member 720. The air inlets 678 andthe fuel inlets 680 are formed in the end wall 674 such that theycommunicate with the first section 738. Thus, air and fuel areintroduced into the first section 738 of the combustion chamber 689. Theair and fuel are introduced into the combustion chamber 689 usingconventional devices, e.g., an injector. An insulation material 736 maybe inserted into the lower region 734 of the combustion chamber 689.

An ignition device 745 is provided and preferably extends through theend wall 674 and into the first section 738. One suitable ignitiondevice 745 is a spark plug device, which upon actuation generates aspark within the first section 738 while air and fuel are beingintroduced through the inlets 678, 680, respectively. As previouslymentioned, a fuel rich mixture is preferably introduced into the firstsection 738 for combustion and an exemplary combustion temperature,which is generated due to the combustion of the air/fuel mixture, isabout 2700°R. The combustion process within the first section 738 formscombustion gases, which flow according to defined flow path, which isindicated by arrows 750. The combustion gases flow around the first end732 of the annular baffle 730 and into the second section 740 of thecombustion chamber 689. The gases then flow up towards the end wall 674and because of the communication between the combustion chamber 689 andthe first ends 702 of the platelet elements 690, the gases flow to thefirst ends 702.

According to the present invention, the channeled platelet elements 690act as heat exchanging elements which replace the conventional functionsperformed by the hot end, cold end, and regenerator of a conventionalStirling engine. As best shown in FIG. 16, each of the channeledplatelet elements 690 has a first heat exchange section 760, a secondheat exchange section 770, and a third heat exchange section 780. Thefirst heat exchange section 760 extends from a first intermediate pointto the first end 702, the third heat exchange section 780 extends from asecond intermediate point to the second end 704 and the second heatexchange section 770 extends between the first and second intermediatepoints. The first heat exchange section 760 comprises a region in whichheat transfer results between the hot combustion gas and a working gas.While helium is a suitable and typically preferred working gas, otherworking gases may be used. For example, hydrogen may be used as theworking gas.

In the first heat exchange section 760, each platelet element 690 has aplurality of working gas channels 800 and combustion gas channels 810formed therein using platelet technology. For example, the number,dimensions, and location of these channels 800, 810 may be tailored byusing precise platelet channel techniques, such as a photo-etchingprocess, a chemical etching process, or a laser cutting process.According to the present invention, the working gas channels 800 aresealed at the first ends 702 of the elements 690, while the combustiongas channels 810 are open at the first ends 702 of the elements 690. Thecombustion gas channels 810 are open at the first ends 702 so that thecombustion gases flow into the channels 810 after the gases exit thecombustion chamber 689. Opposite ends of the channels 810 communicatewith the one or more combustion gas outlets 646 formed in the housing640 so that combustion gases are vented from the platelet elements 690after the gases flow from the first end 702 to the outlet(s) 646.

The working gas channels 800 are likewise formed in the first heatexchange section 760 according to a predetermined pattern in which thechannels 800 and 810 are spaced from another by platelet walls. Theplatelet walls act as heat transfer members so that heat from the hotcombustion gases, flowing through channels 810, is transferred throughthe platelet walls to the working gas contained within and flowingwithin the channels 800. This results in heating of the working gas.Thus, the temperature of the working gas is greater at or near the firstend 702 of the elements 690. For purpose of illustration only, theworking gas may have a temperature of about 720° C. near the first ends702 and as it flows towards the second heat exchange section 770, thetemperature of the gas may decrease to about 680-700° C. in the regionwhere the combustion gases are vented from the elements 690.

FIG. 20A is a cross-sectional view taken along the line 20-20 of FIG.16. However, one will understand that this figure only generallyillustrates the present invention in a very simplified manner. In otherwords, FIG. 20A shows only several working gas channels 800 and onecombustion channel 810. FIG. 20B illustrates an alternative andpreferred cross-sectional view of the first heat exchange section 760.This figure shows that there is a plurality of both combustion gaschannels 810 and working gas channels 800 and that these channels 800,810 are arranged according to a predetermined pattern. In theillustrated embodiment, the channels 800, 810 are generally arranged inalternating columns such that one column of working gas 800 has onecombustion gas channel columns 810 on each side thereof. This permitseffective heating of the working gas flowing within channels 800 as heatfrom the hot combustion gas is transferred across the platelet member690, in which the channels 800, 810 are formed, to effectively heat theworking gas. Once again, FIG. 20B is merely exemplary in nature and itwill be understood that there may be a greater number or a lesser numberof channels 800, 810. Likewise, the channels 800, 810 may be formed inany number of arrangements. In one embodiment, the diameter of each ofthe combustion gas channels 810 is greater than the diameter of each ofthe working gas channels 800. This permits a greater volume of hotcombustion gas to be disposed proximate to the flowing working gas.

Referring now to FIGS. 16 and 21A-21B, unlike the combustion gaschannels 810, the working gas channels 800 are formed in the second heatexchange section 770 so that the heated working gas flows from the firstheat exchange section 760 to the second heat exchange section 770. Thesecond heat exchange section 770 is a working gas regenerator section,which acts similar to a conventional regenerator in a conventionalStirling engine. The second heat exchange section 770 serves to furthertransfer heat between the working gas and the platelet elements 690.More specifically, in this second heat exchange section 770, heat fromthe working gas is transferred to the platelet material forming theelements 690. This results in a continuous reduction in the temperatureof the working gas as the gas flows from an upper end of the second heatexchange section 770 to a lower end thereof.

In one embodiment, the second heat exchange section 770 generally has astacked screen-like configuration where a plurality of the working gaschannels 800 extend therethrough. A matrix or other arrangement of metalstrips may be arranged so as to withdraw heat from the flowing workinggas as it flows through channels 800 from one end of the second heatexchange section 770 to the other. Any number of other heat exchangematerials and configurations may be used so long as the second heatexchange section 770 acts as a heat transfer region between the workinggas and the surrounding platelet structure. It will be appreciated thatthe only channels formed within the second heat exchange section 770 arethe working gas channels 800.

For purpose of illustration only, the working gas may have a temperatureof about 670-700° C. at the upper end of the second heat exchangesection 770 (at or near the interface between sections 760, 770). As theworking gas flows towards the lower end of the second heat exchangesection 770, the temperature of the gas may decrease to about 110-120°C. prior to the gas working entering the third heat exchange section780. It will be understood that these values do not limit the presentinvention in any way and are merely exemplary. The type of working gasand the overall design of the platelet elements 690 will impact thetemperature profile of the flowing working gas.

FIG. 21A is a cross-sectional view taken along the line 21-21 of FIG.16. However, one will understand that this figure only generallyillustrates the present invention in a very simplified manner. In otherwords, FIG. 21A shows only several working gas channels 800 present inthe second heat exchange section 770. FIG. 21B illustrates analternative and preferred cross-sectional view of the second heatexchange section 770. This figure shows that there are a plurality ofworking gas channels 800 formed therein and that these channels 800 arearranged according to a predetermined pattern.

Referring back to FIG. 16, near the upper end of the second heatexchange section 770, a plurality of upper working gas ports 820 areformed in the platelet elements 690. More specifically, each inner face693 of one element 690 contains one or more upper ports 820. The one ormore ports 820 are connected to one or more working gas channels 800such that the working gas freely flows between the ports 820 and thechannels 800. The ports 820 open into an upper end of the piston chamber630 and thus, the ports 820 permit the working gas to freely communicatebetween the upper end of the piston chamber 630 and the working gaschannels 800. Importantly, the ports 820 are formed above the displacerpiston 610 so that axial movement of the displacer piston 610 within thepiston chamber 630 causes redistribution of the working gas in theentire heat exchange system as will be described in greater detailhereinafter.

As one of skill in the art understands, the working gas not only flowsfrom the first heat exchange section 760 to the third heat exchangesection 780, the working gas also flows in an opposite direction withinthe channels 800 due to the axial movement of the displacer piston 630.In this instance, the working gas is heated as it flows through thechannels 800 from the third section 780 to the first section 760.

Because the platelet elements 690 are arranged annularly, the ports 820are radially formed around the piston chamber 630. This permits thedisplacer piston 610 to uniformly distribute the working gas to thechannels 800 of the various individual platelet elements 690 through theports 820.

As illustrated in FIGS. 16 and 22A-22B, the third heat exchange section780 is formed adjacent the second section 770. The third section 780functions as a working gas/coolant heat exchanger. More specifically, aclosed loop cooling system, generally indicated at 830, is provided forcooling the working gas as the gas flows through channels 800 formed inthe third section 780. The cooling system 830 includes a coolant inletconduit 840 and a coolant outlet conduit 850. The inlet conduit 840 isconnected to the one or more coolant inlets 642 of the housing 640 andthe outlet conduit 850 is connected to the one or more coolant outlets644 of the housing 640. The conduits 840, 850 may comprise any number ofsuitable conduit members, e.g., tubing, and the coolant may be anynumber of types of coolant, which is suitable for the intended usedescribed herein. One preferred coolant is water, which is maintainedbelow its boiling point during its flow through the closed loop system830.

The one or more coolant inlets 642 and the one or more coolant outlets644 formed in the housing 640 are in fluid communication with aplurality of coolant channels 860 formed in the platelet elements 690.Thus, each coolant channel 860 is connected at one end to the coolantinlet 642 and at the other end to the coolant outlet 644 so that thecoolant flows through the inlet conduit 840 through the inlet 642 andinto the plurality of coolant channels 860 where the coolant flows tothe outlet 644 and then exits from the housing 640 through the outletconduit 850.

FIG. 22A is a cross-sectional view taken along the line 22-22 of FIG.16. However, one will understand that this figure only generallyillustrates the present invention in a very simplified manner. In otherwords, FIG. 22A shows only several working gas channels 800 and onecoolant channel 860 present in the third heat exchange section 780. FIG.22B illustrates an alternative and preferred cross-sectional view of thethird heat exchange section 780. In FIG. 22B, a plurality of coolantchannels 860 and a plurality of working gas channels 800 are arrangedaccording to a predetermined pattern. For example, the channels 800, 860may be arranged in a number of rows and/or columns. Preferably, thechannels 800, 860 are generally provided in pairs with one working gaschannel 800 facing and being proximately located relative to one coolantchannel 860. In this instance, a wall is provided between the channels800, 860 to not only separate them but also act as a heat transfermember. This wall may be formed of the material, which forms theplatelet and therefore likely resembles a metal strip of materialextending between opposing rows of channels 800, 860.

As the coolant flows through the coolant channels 860, heat istransferred from the proximate working gas to the coolant. The coolantthus experiences a temperature increase as it flows through the channels860. For example when the coolant is water, the water may enter theinlet 642 at a temperature of about 73° C. and then exit through theoutlet 644 at a temperature of about 83° C. This results because heatfrom the working gas is transferred from the working gas through theplatelet element 690 to the water. Conversely, the temperature of theworking gas decreases as the working gas flows through the channels 800.

Referring back to FIG. 16, near the lower end of the third heat exchangesection 780, a plurality of lower working gas ports 870 are formed inthe platelet elements 690. More specifically, each inner face 693 of oneelement 690 contains one or more lower ports 870. The one or more ports870 are connected to working gas channels 800 such that the working gasmay freely flow between the ports 870 and the channels 800. The ports870 open into a lower end of the piston chamber 630 and thus, the ports870 permit the working gas to freely communicate between the lower endof the piston chamber 630 and the working gas channels 800. Importantly,the ports 870 are formed below the displacer piston 610 so that axialmovement of the displacer piston 610 within the piston chamber 630causes redistribution of the working gas in the entire heat exchangesystem as will be described in greater detail hereinafter.

As one of skill in the art understands, the working gas flowsbi-directionally through the first, second, and third heat exchangesections 760, 770, 780 as a result of the axial movement of thedisplacer piston 630. When the working gas flow is from the first end702 to the second end 704 of the elements 690, the temperature of theworking gas progressively decreases, while the opposite is true when theworking gas flows from the second end 704 to the first end 702.

Because the platelet elements 690 are arranged annularly, the ports 870are radially formed around the piston chamber 630. This permits thedisplacer piston 610 to uniformly distribute the working gas to thechannels 800 of the various individual platelet elements 690 through theports 870 when the displacer piston 610 moves axially within the chamber630 away from the combustion member 720.

A pre-heater 900 is preferably provided and disposed around the housing640 so that a pre-heating space 910 is defined between the pre-heater900 and the housing 640. The pre-heater 900 is partially shown in FIG.16. Because of the annular shapes of the defining members, thepre-heating space 910 is also annular in nature. The pre-heater 900includes one or more inlets 912 for receiving ambient air. This ambientair is directed into one or more air channels 928 which communicate atfirst ends thereof with the ignition device 745 so that the air isintroduced into the combustion chamber 689 through the plurality of airinlets 678. According to one embodiment, one or more baffle members 920are provided for separating the combustion gases, which are to beexhausted after exiting the housing 640 through the one or more outlets646, from the ambient air which is introduced through the one or moreinlets 912. The combustion gases are then fed into one or more exhaustchannels 924, which lead to an exhaust vent 926.

At the same time, ambient air flowing through the one or more airchannels 928, flows in the same direction as the exhausted combustiongases. Preferably, the air channels 928 and the exhaust channels 924 areparallel to one another and in one embodiment, the channels 924 and 928are formed in an alternating manner. However, it will be understood thatthe exhaust channels 924 are open at or near the first end 670 of thehousing 640, while the ambient channels 928 are closed in this regionand instead lead to the ignition device 745.

Because of the high temperatures at which other components of theStirling engine operate at, it is preferred to maintain the heatexchanging components, e.g., the platelet elements 690, at elevatedtemperatures also to reduce thermal stress, etc. This is achieved bypreheating the ambient air introduced to the combustion chamber 689. Theambient air is preheated by using heat transfer between the combustiongases, which are being exhausted. In other words, by disposing the airchannels 928 in close proximity to the exhaust channels 924, the ambientair is heated by the combustion gases as it flows to the combustionchamber 689. This further increases the overall efficiency of the entireStirling engine since the benefits of heat transfer are optimized in asmany different regions and by as many different operations as possible.In other words, the heat of the exhaust gases is not wasted, but ratheris used to perform an additional heat transfer, which results in moreefficient combustion and also reduces the risk that there will be agreat temperature difference between the heat exchanger components ofthe Stirling engine and the other components thereof.

FIG. 23 shows a number of channeled platelet elements 690 which areadapted to be positioned in an annular manner around the combustionmember 720 to form the piston chamber 630. Each individual plateletelement 690 may or may not have a different channel structure thanadjacent platelet elements 690. In other words, the logic of thechannels is tailored to provide the desired flow of the working gas,combustion gas, and the coolant. FIG. 23 illustrates that each of theelements 690 has the first heat exchange (HEX) section 760, the secondheat exchange section 770, and the third heat exchange section 780.Because of precision of the platelet formation technology, very smalldiameter channels may be formed in the platelet substrate and the layersof each individual channel may be constructed so that the fluid flowsaccording to the defined logic of the channels. For example, some of thechannels may communicate with channels formed in other layers so thatthe fluid can flow through multiple layers and in another embodiment, atleast some of the channels in one layer do not communicate with some ofthe channels in the other surrounding layers. In yet another aspect,some of the channels, generally indicated at 901, are formed in each ofthe individual platelet elements 690 such that a radial flow channel isformed around the displacer chamber 630.

The general operation of a Stirling engine having the heat exchangingcomponents thereof formed of platelet elements 690 will now be describedwith reference to FIGS. 16-23. As previously mentioned, the Stirlingengine of the present invention operates in essentially the same manneras a conventional Stirling engine with the exception that the hot andcold end of the heat exchange system are different. The displacer piston610 serves to move the working gas through the working gas channels 800and through the piston chamber 630. As best shown in FIG. 16, the onlychannels which are in fluid communication with the piston chamber 630are the working gas channels 800. Thus, the piston chamber 630 is partof the closed loop working gas flow path.

As those of skill in the art will appreciate, the working gas flows in abi-directional manner through the channels 800. The upper and lowerports 820, 870 permit the working gas to enter and exit the pistonchamber 630 through each of the respective ports 820, 870 depending uponthe flow direction of the working gas. In a first position, thedisplacer piston 610 is in an up most position in which the displacerpiston 610 is just below the upper ports 820. In a first stage, oftenreferred to as an isothermal compression stage, the displacer piston 610is in the up most position and the working piston 620 is directed towardthe displacer piston 610 by action of the flywheel, etc. The distancebetween the displacer piston 610 and the working piston 620 decreasesand this causes working gas to flow out through the ports 870 and intochannels 800. The working gas is compressed under pressure underconstant volume. In this stage, the working gas is generally flowingupward through the channels 800 from the third heat exchange section 780to the first heat exchange section 760 and the regenerator (second heatexchange section 770) serves to supply heat to the working gas as itflows toward the first heat exchange section 760 and also into the upperports 820 so that the hot gas flows into the combustion chamber 630above the displacer piston 610. In addition, the working gas is heatedby the hot combustion gas flowing through channels 810. This correspondsto an isothermal expansion stage of the Stirling cycle and duringisothermal expansion, the volume of the working gas expands due to theheating. In this stage, the displacer piston 610 moves downward in thechamber 630 toward the working piston 620. This movement of thedisplacer piston 610 causes the working gas to flow in an oppositereverse path such that the hot working gas flows downward in channels800 through the first heat exchange section 760 to the third heatexchange section 780. As the working gas flows in this direction, theregenerator (second heat exchange section 770) serves to store heat asthe working gas flows from the hot expansion space (first section 760)to the cool compression space (third section 780). This results in theworking piston 620 being directed downward away from the displacerpiston 610 resulting in the distance between the two pistons 610, 620becoming greater as the displacer piston 610 reaches its lowermostposition. Cold working gas enters through ports 870 below the displacerpiston 610 but above the working piston 620.

This working gas cycle continuously proceeds so that the working gasflows through the regenerator (second heat exchange section 770) fromthe hot expansion space to the cool compression space resulting in theregenerator storing heat. The working gas then reverses its flow paths,due to the movement and action of the displacer piston 610, so that itflows from the cool compression space to the hot expansion space and theregenerator returns the heat to the working gas. This cycle of theworking gas is continuously repeated as the pistons 610, 620 moveaxially in the chamber 630. By incorporating platelet technology intothe hot and cold end heat exchangers of the Stirling engine, heattransfer efficiency is significantly improved resulting in a moreefficient running engine. The present invention provides a robust/longlife metal cooling capability by incorporating the internal region ofthe Stirling displacer cylinder head end in the platelet stack. FIG. 16illustrates a flat cylinder head end; however, the cylinder head end maybe domed-shaped instead. Platelet technology permits the coolant/workinggas heating passages to be made with hundreds of small openings in thehead end and thus eliminate the need for the present day ceramicinsulation. This reduces the cost of the entire head end. The presentinvention also provides for an even, more effective and efficient heattransfer surface area and results in a more compact and lighter weightoverall Stirling engine.

Furthermore, while the present invention illustrated in FIG. 16 shows aheat exchange structure which functions in a series fashion, it iswithin the scope of the present invention to provide the samefunctionality in a parallel configuration. For example, concentriccylinders may be provided with the working gas/water heat exchanger aninner diameter, followed by the working gas regenerator in the centercylinder and then the hot gas/working gas heat exchanger as theoutermost cylinder. It will be appreciated that the concentric cylindersmay be ordered in other alternative configurations.

FIG. 24 illustrates another aspect of the present invention. The presenttechnology for conventional Stirling engines utilizes a single stagecombustion process. High emission levels of CO and NO, are a criticalenvironmental concern. Design approaches such as exhaust gasrecirculation (EGR) or combustion gas re-circulation (CGR) have beenused to reduce the emission of NO_(x). Neither approach to date canachieve acceptable emission levels without sacrificing performance orincurring high parasitic pressure losses. According to anotherembodiment, the present invention provides a multi-stage combustorsystem, generally indicated at 1000. The multi-stage combustor system1000 significantly reduces the emission level while maintaining highsystem performance and long hardware life.

In a first embodiment of the multi-stage combustor system 1000, shown inFIG. 24, a two-stage combustion process without inter-stage cooling ispresented. FIG. 24 illustrates generally the heat exchange components ofthe multi-stage combustor system 1000. The heat exchange components ofthe multi-stage combustor system 1000 include the first section 760 andthe second section 770 (regenerator). The third section 780 (FIG. 16) isnot present in this embodiment since this embodiment does not includeinter-stage cooling. The first section 760 has a plurality of workinggas channels 800 which extend into the second section 770 and alsoincludes a plurality of the combustion gas channels 810.

The multi-stage combustor system 1000 includes a first (primary)combustor 1010 and a second (secondary) combustor 1020. The firstcombustor 1010 is coupled to a fuel injection/ignition device 1030. Thedevice 1030 includes a number of fuel channels 1032 and air channels1034, which serve to provide fuel and air to the first combustor 1010.An ignitor 1036 provides a spark or the like to ignite the fuel/airmixture to generate heat and combustion gases. The first combustor 1010can either operate at fuel-rich conditions or at the stoiochiometricpoint where the mixture has equal fuel and air components. Preferably,the first combustor 1010 operates at fuel-rich conditions. The NO_(x)emission is very low in the first combustor 1010 due to the lack ofextra oxygen. In the first combustor 1010, the gas has a firsttemperature and in one embodiment, the first temperature is about3000°R.

After exiting the first combustor 1010, secondary air is introduced at1040 into the second combustor 1020. This secondary air is rapidly mixedto dilute and reduce the combustion temperature while maintaining theNO_(x) emission at the low level (as shown in FIG. 25). This results inthe present multi-stage combustor system 1000 simultaneously achievinghigh system performance and low NO_(x) emission level. Since theresidence time for CO formation is long, CO will be converted to CO2 inthe platelet passages (combustion channels 810) before being exhausted.In the second combustor 1020, the gas has a second temperature, which isless than the first temperature in the first combustor 1010. Forexample, the second temperature is less than 3000°R.

FIG. 25 illustrates the advantages provided by the systems according tothe present invention. More specifically, FIG. 25 illustrates the CO andNO, variation with air and NG flow ration. The stoiochiometric point isalso shown where the fuel and air components are about the same.

FIG. 26 shows another embodiment of the present invention in which amulti-stage combustor system, generally indicated at 1100 is provided.The system 1100 significantly reduces the emission level whilemaintaining high system performance and long hardware life.

In a first embodiment of the system 1100, shown in FIG. 26, a two-stagecombustion process with inter-stage cooling is presented. FIG. 24illustrates generally the heat exchanging components of the multi-stagecombustor system 1000. The heat exchanging components of the multi-stagecombustor system 1000 include the first section 760 and the secondsection 770 (regenerator) and the third section (not shown). The system1100 includes a first combustor 1110 and a second combustor 1120. Thefirst combustor 1110 includes the fuel injection/ignition device 1030for injecting fuel and air into the first combustor. The first combustor1110 operates at fuel-rich conditions with gas temperature between about2500°R to 3000°R. The hot combustion gases flow through the channel 810in the first section 760 before being exhausted. As previously describedin great detail, the flow of the hot combustion gases in the firstsection 760 transfers heat to the working gas, which is flowing inproximate working gas channels 800. After transferring energy to theworking gas inside the heat exchanger, the combustion gas temperaturedeceases while maintaining the fuel-rich status.

According to this embodiment, a secondary air injection system 1200injects air into the flowing combustion gases as it flows through thefirst section 760. By introducing secondary air, the gas temperature isbrought back to the original design gas temperature of about 2500°R toabout 3000°R because of the energy created by additional burning of thegas. The heat transfer mechanism from hot gas to working gas resumesbeyond this point. This process of adding secondary air can be repeatedseveral times, as required, with combustion gas temperature alwaysstaying below 2500°R, to 3000°R. The NO_(x) emission level can bemaintained at very low levels since the gas temperature during theentire combustion and heat transfer process is maintained at atemperature below the NO_(x) kinetic threshold. A two-stage combustionprocess with inter-stage cooling according to one embodiment is shown inFIG. 26.

Accordingly, FIGS. 24-26 illustrate two exemplary multi-stage combustionsystems, which offer the following significant advantages. First, thefirst stage of burning takes place at a low air/fuel ratio. This resultsin a cooler flame temperature and results in a more durable combustionchamber and working gas heat exchanger. Second, the overall volume ofthe cooler fuel rich gas is less than would be required if astoiochiometric mixture of air was used for initial combustion. Thisresults in a significantly lower temperature hot gas than would begenerated by cooling the combustion with the addition of exhaust gasrecirculation (EGR). Third, the staging of the combustion with theaddition of more combustion air at about half way through the plateletstack heat exchanger provides for a more uniform heat input to theworking gas heat exchanger at a time and place where the fuel rich gashas been cooled to just above the temperature necessary to re-ignite thefuel rich gases.

Fourth, the second stage of combustion is thus significantly reduced intemperature compared to the stoiochiometric value that would haveoccurred if the first stage combustion had not been cooled down byheating the working gas. Fifth, the significantly cooler thanstoiochiometric combustion described above results in significantly lessNO_(x) formation and therefore a much cleaner final exhaust.

Now referring to FIGS. 27-29, a combustion device 1300, a plateletworking gas heat exchange plate 1400, a platelet manifold 1500 and aplatelet air injector 1600 according to another embodiment of thepresent invention are presented. The device 1300, plate 1400, manifold1500, and injector 1600 are intended to be used at the hot end of aStirling engine and more specifically, these components operativelycommunicate with a displacer piston cylinder 1310. As with previousembodiments, the Stirling engine includes a number of heat exchangers,which act to transfer heat to and from the working gas as it flows. Apiston chamber 1320 is provided and formed in the cylinder 1310 with thedisplacer and working pistons (not shown) being axially moved therein.These pistons function in the manner previously described. The pistonchamber 1320 is defined at one end by a head end 1330 of the cylinder1310, which in the case is dome shaped; however it may have a flatshape.

The cylinder 1310 may be formed conventionally using metal or the likeor it may be formed of a series of stacked platelets having the desiredchannels formed therein using platelet technology. A first heat exchangesection 1340 extends from one face 1401 of heat exchange plate 1400 to asecond heat exchange section (regenerator) 1350. The first heat exchangesection 1340 contains the heat exchange plate 1400, the manifold 1500 aswell as the working gas channel 1342. The second heat exchange section1350, in the exemplary embodiment, is thus located in series below thefirst heat exchange section 1340. The heat exchange plate 1400 in thefirst Heat exchange section 1340 serves as a heat transfer mechanismbetween combustion gases and the working gas, while the second heatexchange section 1350 acts as a regenerator where heat is transferredfrom or to the working gas. According to one embodiment, the regenerator1350 comprises a screen like structure 1352 having a plurality ofpassages defined thereby. The working gas flows through these passagesdefined by the screen structure 1352. However, it will be appreciatedthat the screen structure 1352 may instead be formed of a plateletmember, such as the second section 770 of the elements 690 shown in FIG.16.

The working gas channel 1342 extends through the regenerator 1350 to thefirst section 1340. The working gas flows through this channel 1342.According to the present invention, a platelet working gas manifold 1500is disposed on and bonded to the displacer piston cylinder 1310. Themanifold 1500 is formed of a number of laminated diffusion bonded metalplatelets that contain many manifold passageways 1502 which are formedusing platelet technology. For example, the passageways 1502 may beformed by a chemical etching process and are utilized in the head enddome of the Stirling cycle engine. The manifold 1500 is bonded directlyto the displacer piston cylinder 1310 and serves to distribute workinggas to the plate 1400 as will be described. As shown in FIG. 27, thepassageways 1502 are both horizontally and vertically formed. At leastsome of the vertically orientated passageways 1502 open into the pistonchamber 1320. This serves as the means for introducing working gas abovethe displacer piston (not shown). The passageways 1502 are thus in fluidcommunication with the channel 1342 to distribute the working gas over alarge area of the displacer piston cylinder 1310.

The working gas heat exchange plate 1400 is disposed above the manifold1500 and preferably is bonded thereto. One exemplary plate 1400 is bestshown in FIG. 28. The plate 1400 may comprise a flat disk metal plateletor it may be in the form of a bent and pleated cup shaped heatexchanger. The later embodiment resembles a plurality of stacked andbonded tin foil muffin cups and thus, this embodiment may be referred toas a “muffin liner” heat exchanger configuration. As best shown in FIG.28, the exemplary plate 1400 has an annular disk having a plurality ofchannels 1410 formed on at least one surface thereof. Because of theannular shape of the plate 1400, the channels 1410 are radial channels,which extend from a center region 1412 of the plate 1400 to an outeredge 1414 of the plate 1400. The width of the channel 1410 may varyalong the length thereof and in the illustrated embodiment, the channel1410 has a greater diameter near the outer edge 1414 than at the centerregion 1412.

Because the plate 1400 is disposed on top of the manifold 1500, thepassageways 1502 are provided with small entrance ports, which are influid communication with at least some of the channels 1410. Inaddition, the channel 1342 is also in fluid communication with the plate1400 and actually the channel 1342 delivers the working gas to the plate1400. The working gas then flows through the great number of channels1410 before flowing through the entrance ports and into the passageways1502 of the manifold 1500 and then ultimately into the piston chamber1320.

One face 1401 of the plate 1400 faces a combustion chamber 1390, whichcontains hot combustion gases. The flowing hot combustion gases transferheat to the working gas flowing through the channels 1410. By providinga great number of radial channels 1410, the working gas is effectivelyand uniformly distributed and heated and then delivered to the manifold1500 where the hot working gas is then delivered to the piston chamber1320. When the working gas flows in the reverse direction during theoperation of the Stirling engine and more specifically in response tomovement of the displacer piston (not shown), the opposite occurs inthat the working gas is heated as it flows along the channels 1410 tothe channel 1342 before flowing to the regenerator 1350, where theworking gas experiences a significant decrease in temperature due toheat transfer. The effective heat transfer that is provided by the plate1400 eliminates the need for the present day ceramic insulationtechnology normally used in the hot end of the Stirling engines. It alsoprovides for a more effective and efficient heat transfer surface arearesulting in a more compact and lighter weight hot end. The channels1410 formed in the plate 1400 thus act as heat transfer passageways toefficiently heat the working gas and to provide metal coolingcapability.

The combustion device 1300 includes an injector/ignition device 1309,which acts to provide fuel and air to the combustion chamber 1390. Thedevice 1309 has a body, which defines the combustion chamber 1390 andgenerally has an annular shape. The body has a sidewall 1317, which hasformed therein a pre-heated air channel 1319. Extending between thesidewall 1317 is a platelet member 1321, which actually forms an upperwall enclosing the combustion chamber 1390. The platelet member 1321 hasa plurality of fuel channels 1323 and a plurality of air channels 1325formed therein for delivering fuel and air to the combustion chamber1390. In addition, the device 1309 includes an ignitor 1327, e.g., aspark plug, which causes combustion of the fuel/air mixture. By usingplatelet technology, the channels 1323, 1325 are carefully formed andtailored to provide the desired fuel/air mixture. For example andaccording to one embodiment, a fuel rich mixture is provided to thecombustion chamber 1390. In one embodiment, the mixture is about 40% airand 60% fuel and the temperature within the combustion chamber 1390 isabout 2700°R. Opposite the platelet member 1321, the combustion chamber1390 opens into a space 1331, which is above the face 1401 of the plate1400. Thus, the hot combustion gases are in contact with the face 1401and this results in heat transfer from the hot combustion gases throughthe plate 1400 to the working gas flowing therein. Because of theannular nature of the plate 1400 and the combustion device 1300, thespace 1331 is also annular in nature. The platelet air injector 1600forms a part of the combustion device 1300 and is in communication withthe preheated air channel 1319. Thus, the space 1331 is defined betweenthe platelet air injector 1600 and the plate 1400 and the hot combustiongases are channeled through this space 1331 to an exhaust manifold 1700.As best shown in FIG. 27, the manifold 1700 defines an exhaust channel1702 for delivering the combustion gases to one or more exhaust ports1704.

The air injector 1600 is formed of a plurality of bonded platelets. Thecombustion device 1300 also has an associated ambient air manifold 1800,which directs ambient air into an ambient air channel 1802, whichdirects air into a pre-heater device, generally indicated at 1900. Theambient air manifold 1800 has a complementary shape to the exhaustmanifold 1700 and in one embodiment, is disposed around the exhaustmanifold 1700. Both manifolds 1700, 1800 are generally annular membersdisposed around the cylinder 1310 and extend upwardly toward theplatelet member 1321. Because of the close relationship between themanifolds 1700, 1800, the ambient air flowing through the channel 1802is heated by the hot combustion gases that are exiting the combustionchamber 1390 through the exhaust channel 1702.

This partially heated ambient air is delivered to the pre-heater device1900, which is generally disposed above the air injector 1600. Thepre-heater device 1900 receives the partially heated ambient air andacts to provide additional heat to the ambient air. The device 1900 isoperatively connected to a plurality of air orifices 1610 formed in theplatelet injector 1600. The air orifices 1610 are formed in the plateletstructure and provide entrances into the space 1331, where the hotcombustion gases are flowing from the combustion chamber 1390. Thus, theair orifices 1610 are designed to provide multi-stage micro-combustorair injection “staging” of the combustion with the addition of morecombustion air (the pre-heated ambient air) as it passes over the face1401 of the plate 1400. This design provides for a very uniformtemperature and heat input to the plate 1400 and also the combustiongases are continuously maintained at a temperature well above thetemperature necessary to re-ignite the fuel-rich gases. By successivelyfeeding ambient air into the combustion gases, additional combustionoccurs resulting in the combustion gases maintaining heat instead ofhaving a decreasing temperature due to loss of heat to the plate 1400.In this manner, the combustion gases flow into the exhaust channel 1702at a temperature much greater than would have been the case had thecombustion gases simply flowed from the combustion chamber 1390 and overthe plate 1400, where heat transfer takes place. By maintaining theexhaust gases at elevated temperatures, the ambient air flowing into thechannel 1802 is more effectively heated.

The air injector 1600 is essentially a platelet manifold that providesair to the fuel rich unburned combustion gases and in combination withthe device 1900 serves to pre-heat the incoming ambient air. Allaugmentation air is injected from swirler orifices 1610 that areregeneratively cooled as best shown in FIG. 29. FIG. 29 illustrates thatthe orifices 1610 may have different sizes and the number of orificeswill likely vary depending upon the size and shape of the orifices 1610.The air is then aimed at the face 1401 of the plate 1400 to enhancecombustion mixing and aid in heat transfer. In addition, by encasing theplate 1400 (which reaches high temperatures) and the upper end of thehot end with the pre-heater 1900 and the ambient manifold 1800, theouter surfaces of the system are maintained near ambient temperatureconditions thus eliminating the need for external protective insulation.

This embodiment utilizes multi-staged micro-combustion for burning thefuel rich gas to completion resulting in significant advantages. First,the initial stage of the burning takes place at a low fuel/air ratio.This results in a cooler flame temperature and results in more durablefuel and air injectors, combustion chamber walls, and helium heatexchanger walls. Second, the overall combustion gas volume required bythe multi-stage combustor is much less than a conventional burner designfor several important reasons. This type of combustor has a much coolerinitial fuel rich gas combustion stage which has much less volume thanwould be required in 100% of the air required for stoiochiometriccombustion were used for initial stage combustion. The combustionrequires less volume because the combustion gases are much denser sincethey are cooler than stoichiometrically burned gases and the combustiongases do not contain any exhaust gas recirculation, a technique commonlyused to cool the combustion gases.

Furthermore, this approach maintains the combustion process at an almostconstant temperature which is much cooler than the stoiochiometric valuethat would have occurred if the combustion had taken place in one stepand gases had not been continuously cooled down by transferring heat tothe plate 1400 and then being reheated in multiple micro-combustionstages. Each orifice 1610 may be thought of as being associated with onemicro-combustion stage in which the gas is reheated by introducingambient air to the combustion gases causing more combustion. The uniformlower combustion gas temperature reduces the thermal gradients in thestructural components forming both the plate 1400 and the staged airinjection manifold 1600 and the pre-heater 1900. The cooler multi-stagemicro-combustion process results in significantly less NO_(x) formationand therefore provides a cleaner final exhaust.

It will also be appreciated that the platelet principles discussedherein may be adapted to provide a multiple cylinder platelet hot end.In Stirling engines that have multiple cylinders, each cylinder willhave its own platelet hot end. Conventionally, multiple cylinderStirling engines have used a single hot end serving all cylinders of theengine. There are several disadvantages associated with a constructionwhere one hot end is used to supply the heat for all cylinders. First,the efficiency of the system is usually not optimized as heat is wastedbecause of the size of the hot end, which is needed to supply heat toall cylinders. Second, the maintenance and repair of this single hot endand the cylinders themselves are difficult because the single hot endserves all cylinders and therefore must be dealt with during maintenanceor repair of any of the cylinders.

In contrast, the platelet hot end construction disclosed herein providesa more modular type arrangement in that each cylinder has its ownplatelet hot end unit. In other words, the device shown in FIG. 27 isused with one cylinder and each cylinder has its own corresponding hotend unit formed of platelets. This provides greater efficiency andversatility. Because each cylinder is powered by its own closed loopplatelet hot end unit, the efficiency of the overall Stirling engine isincreased because the energy waste per each cylinder is significantlyreduced. In other words, a reduction in the amount of energy wasted inthe operation of each cylinder results in increased operatingefficiency.

Another advantage is that the modular type arrangement permits onemodular hot end unit to be repaired or replaced without requiring theother hot end units to be taken apart or otherwise disrupted. Forexample, if one cylinder needs to be repaired, the platelet hot end unitfor this particular unit is removed or otherwise worked on, while theother platelet hot end units are left in tact.

FIG. 30 illustrates another embodiment of a Stirling engine constructedusing a platelet design and having a heat transfer manifold or hot end2000. This embodiment is similar to the embodiment shown in FIGS. 27-29and therefore like components are numbered alike and will not bediscussed in any detail. The major difference between the hot end 2000of FIG. 30 and the hot end constructions of the previously-discussedembodiments is the manner of heating the working gas. The priorembodiments were combustion based systems having a combustion device,such as device 1300 of FIG. 27, which served to convert fuel into heatwhich was then transferred to the working gas as it flowed throughdiscrete channels formed in the platelets at the hot end. The hot end2000 of this embodiment eliminates the combustion device 1300 andinstead uses solar energy as the means for heating the working gasflowing through the platelet manifold 1400.

The solar hot end 2000 may be constructed in a similar manner as theembodiment in FIG. 27 with the exception that the upper portion of thehot end 2000 is the working gas heat exchange plate 1400 instead of thecombustion device 1300, which is eliminated. The heat exchange plate1400 may have the construction shown in FIG. 28 or it may have adifferent construction. The heat exchange plate 1400 is disposed on topof the manifold 1500. Channels formed in the heat exchange plate 1400are in fluid communication with passageways 1502 formed in the manifold1500. The working gas is thus permitted to flow within a circuit definedby the piston chamber 1320, the manifold 1500, the heat exchange plate1400 as well as the working gas channel 1342 which are part of the firstheat exchange section 1340.

In this embodiment, the one face 1401 of the heat exchange plate 1400 isan exposed surface of the hot end 2000. A solar focusing unit 2010 isused to focus sunlight directly on the one face 1401 so as to provide anenergy source for heating the working gas (e.g., helium) as it flowsthrough the numerous intricate channels formed in the heat exchangeplate 1400. The solar focusing unit 2010 may comprise any number ofcommercially available units, which act to focus sunlight into aconcentrated area, in this case the one face 1401 of the heat exchangeplate 1400. The solar focusing unit 2010 will normally include some typeof mirror array or lens construction, which focuses sunlight onto asmall, precise area at an elevated intensity. For example, some lensesare available that can concentrate the sunlight to 20 times its normalintensity.

It will be appreciated that the precise type and strength of the lens orother components of the solar focusing unit 2010 will depend and varyfrom application to application. For any given application, the solarfocusing unit 2010 can be optimized by focusing sunlight of an optimizedintensity on the one face 1401. One of skill in the art will understandthat solar units have different maximum intensity values. It isdesirable to optimize the sunlight intensity and other characteristicsof the focused sunlight in order to optimize efficiency of the workinggas heat transfer operation and thus optimize the efficiency of theStirling engine itself. If the sunlight intensity is too high, then theheat exchange plate 1400 or other components may become damaged byexposure to excessive heat. Conversely, if the sunlight intensity is toolow, then an inefficient heating of the working gas results because theheat transfer to the working gas is less than optimized. This results inthe working gas not reaching the desired temperatures to ensure optimaloperation of the Stirling engine.

FIG. 31 illustrates a working gas heat exchange plate 2100 of anotherembodiment. In one embodiment, the heat exchange plate 2100 is used inplace of the heat exchange plate 1400 (FIG. 27 and FIG. 30) andaccordingly, is designed to provide fluid flow of the working gas fromand to the other components of the system. The exemplary heat exchangeplate 2100 has a first face 2110, which is designed to face away fromthe piston chamber 1320 (see FIG. 30) and a second face 2120, whichfaces the piston chamber 1320 and is disposed over the manifold 1500.The heat exchange plate 2100 is an annular shaped disk consists of twoor more individual platelets. The individual platelet has a plurality ofchannels formed in the first face 2125. More specifically, the channelsare arranged in two discrete radial circuits. A first outer circuit,generally indicated at 2130, is formed of a plurality of first channels2140 and a second inner circuit, generally indicated at 2150, is formedof a plurality of second channels 2152. Optionally, channels (not shown)can be formed in the face 2110 to reduce the mass of the plate 2100.These channels may have a similar pattern as the channels 2140, 2152 orthey may assume other patterns. By forming channels in the face 2110,the overall weight of the plate 2100 is advantageously reduced withoutjeopardizing the performance thereof. The channels in the face 2110 alsoincrease heat transfer by creating turbulent flow and simultaneouslyreducing the wall thickness of the channels 2140 and 2152.

The first and second circuits 2130, 2150 are arranged in a concentricmanner in the illustrated embodiment. Each channel 2140 of the firstouter circuit 2130 is kept separate from the other channels 2140 andincludes a first end 2142 and a second end 2144. The channel 2140 isformed in a looped configuration where the first and second ends 2142,2144 are proximate one another. Because of the annular shape of theplate 2100, the channels 2140 are radially formed and in one aspect ofthis embodiment, the spacing between adjacent channels 2140 is keptconstant. As best shown in FIG. 31, each channel 2140 has a generallyelongated, narrow U-shape, which is radially curved also. The channels2140 are formed within the heat exchange platelet 2100 using any numberof techniques described hereinbefore. Platelet techniques permitdiscrete, small dimension channels to easily be formed in the plateletsubstrate, which in this case is the heat exchange plate 2100.Therefore, the precise spacing between the channels 2140, the number ofchannels 2140, and the shape and dimensions of the channels 2140 can becarefully controlled and tailored. Each of the channels 2140 preferablyhas the same length.

The second inner circuit 2150 is formed within the center of the firstouter circuit 2130. The plurality of channels 2152 are also formed in aradial arrangement within the heat exchange plate 2100. In one exemplaryembodiment, the channels 2152 are arranged in a swirl-like pattern witheach channel 2152 having a first end 2154 and a second end 2156. Thefirst ends 2154 converge toward the center of the heat exchange plate2100, while the second ends 2156 define an outer edge of the first innercircuit 2150. Each channel 2150 is formed with a defined curvature andpreferably the defined curvature for each channel 2150 is the same sothat each of the channels 2150 has the same length. The channels 2150should be formed so that each is curved in the same direction, therebyproviding the swirl-like pattern. The second ends 2156 are formedproximate to the first and second ends 2142, 2144 of the channels 2140.

The spacing between the channels 2152 is kept constant. The spacingbetween the channels 2152 does not necessarily have to be the same asthe spacing between the channels 2140. In the illustrated embodiment,the spacing between the channels 2152 is greater than the spacingbetween the channels 2140. Accordingly, each of the circuits 2130, 2150maintains a constant spacing between its own channels 2140, 2152,respectively. This spacing is a function of the radius.

In another aspect, the length of each of the channels 2140 is aboutequal to the length of each of the channels 2152. The swirl-like patternof this embodiment permits not only a dual circuit construction but alsopermits the lengths of the channels 2140, 2152 to be greater than thechannel lengths of prior embodiments, such as the embodiment of FIG. 27.The channels of FIG. 27 are more of a linear spoke-like fashion, whichreduces the overall length that each of them can assume.

The swirl-like pattern of FIG. 31 provides an advantageous arrangementbecause efficient heat transfer is a function of the number of channelsin which the fluid flows and also the lengths of the respectivechannels. By increasing the length of the channels and maintaining agreat number of channels, more efficient heat transfer is realized. Inone embodiment, the surface area of the channels 2140 is approximatelythe same as the surface area of the channels 2152. In this embodiment,the fluid (e.g., the working gas), which flows within the heat exchangeplate 2100, is delivered to the plate 2100 such that approximately halfof the fluid (by volume) is directed into the first outer circuit 2130,while the other half of the fluid is directed into the second innercircuit 2150.

In order to accomplish this, the heat exchange plate 2100 is fluidlyconnected to the other components of the hot end (e.g., the manifold1500) such that discrete fluid passageways fluidly communicate with thechannels 2140 and other discrete fluid passageways fluidly communicatewith the channels 2152. For example, the passageways 1342 (FIG. 27) maybe fluidly connected to the channels 2140 while the channels 1502 (FIG.27) may be in fluid communication with the channels 2152.

The use of a dual circuit flow construction within the heat exchangeplate 2100 provides increased versatility and design options. Morespecifically, the components of the hot end, such as the manifold 1500,can be tailored to provide inlets and outlets connected to each of thefirst outer circuit 2130 and the second inner circuit 2150. Improvedheat transfer results because the fluid (e.g., the working gas) isspread out over a great number of channels 2140, 2152 and is exposed toeither a combustion device (FIG. 27) or a solar focusing unit (FIG. 30)which transfers heat energy to the fluid. The heat exchange plate 2100also results in a more elastic working gas heat exchange structure sincethe heat exchange plate 2100 provides more opportunity for channels tobe formed therein resulting in increased flexibility.

Another advantage of the dual circuit configuration of FIG. 31 is thatit provides adequate bonding surface area between channels 2140 andbetween channels 2152. As with the heat exchange plate 1400 of FIG. 27,the heat exchange plate 2100 of FIG. 31 is disposed on top of themanifold 1500, which is also formed of a platelet construction.Accordingly, the heat exchange plate 2100 is bonded to the plateletmanifold 1500 using the techniques described hereinbefore. In order toensure a strong bond between the heat exchange plate 2100 and themanifold 1500, an adequate bonding surface needs to be provided on eachmember so that these surfaces mate together and bond together during thebonding operation. The heat exchange plate 2100 provides a bondingsurface, which is preferably uniform across its diameter. By havingconstant spacing between the channels 2140, 2152 of each of the circuits2130, 2150, a uniform bonding surface area is provided within each ofthe circuits 2130, 2150 between the channels 2140, 2152. In contrast,the plate 1400 of FIG. 28 does not have a uniform bonding area as theouter radial spacing between the channels 1410 is greater than the innerradial spacing between the channels 1410. This results in the outerradial edge of the plate 1400 having more bonding surface area than theinner radial edge of the plate 1400.

FIGS. 32-34 illustrate a bi-directional fluid transfer duct, generallyindicated at 2200. In fluid and thermal management systems, the occasionmay arise where a hot (or cold) fluid must first flow in one directionthen reverse flow in the opposite direction. Furthermore, it may bedesirable to have a second fluid circuit also flow in the system eitherbi-directionally or uni-directionally. This second fluid circuit definesa flow path for a second fluid, which can be at a different temperaturethan the first fluid flowing in the first fluid circuit. The secondfluid can flow in either one or both directions in the second fluidcircuit. It may be further advantageous to either enhance heat transfer(heat exchange) or thermally insulate temperature differential betweenthe two fluid streams while in transit.

FIG. 32 is a top plan view of the bi-directional fluid transfer duct2200. The duct 2200 includes a first annular wall 2210, a second annularwall 2220, and a third annular wall 2230. Preferably, the first, second,and third annular walls 2210, 2220, and 2230 are concentric with respectto one another. In this embodiment, the first annular wall 2210 is anoutermost member, the third annular wall 2230 is the innermost member,and the second annular wall 2220 is an intermediate member. Each of thefirst, second, and third walls 2210, 2220, and 2230 may be thought of asbeing a cylindrical structure.

The duct 2200 further includes a first heat exchange element 2240 and asecond heat exchange element 2250. The first heat exchange element 2240defines a first flow circuit and the second heat exchange element 2250defines a second flow circuit. The first heat exchange element 2240 isdisposed between the first annular wall 2210 and the second annular wall2220 and the second heat exchange element 2250 is disposed between thesecond annular wall 2220 and the third annular wall 2230. In oneembodiment, the first and second heat exchange elements 2240, 2250 eachis in the form of a corrugated metal sheet.

The first corrugated heat exchange element 2240 defines two distinctfluid circuits, namely first fluid circuits 2260 and second fluidcircuits 2270. The first fluid circuits 2260 generally border the firstannular wall 2210 and the second fluid circuits 2270 generally borderthe second annular wall 2220. In the exemplary embodiment, each of thefluid circuits 2260, 2270 is generally pie-shaped with thecross-sectional area of the first fluid circuit 2260 being greater nearthe first annular wall 2210 and the cross-sectional area of the secondfluid circuit 2270 being greater near the second annular wall 2220. Itwill be understood that the term “fluid” describes any number of fluidsthat are suitable for flowing within the first and second flow circuits.For example, the fluids may be in a liquid form, a gaseous form, or acombination thereof or in another form in which the fluid can flowwithin the flow circuits. In one embodiment, a gas, such as air, flowswithin the first flow circuit and a gas or liquid flows within thesecond flow circuit. In another embodiment, a liquid, such as water,flows within the first flow circuit and a gas flows within the secondflow circuit.

Similarly, the second corrugated heat exchange element 2250 defines twofluid circuits, namely third fluid circuits 2280 and fourth fluidcircuits 2290. The second corrugated heat exchange element 2250 isdisposed between the second and third annular walls 2220, 2230 such thatthe third fluid circuits 2280 generally border the second annular wall2220 and the fourth fluid circuits 2290 generally border the thirdannular wall 2230. In this embodiment, the third and fourth circuits2280, 2290 are also pie-shaped with the third fluid circuits 2280bordering the second fluid circuits 2270. In the illustrated embodiment,each of the first, second, third and fourth fluid circuits 2260, 2270,2280, 2290 has the same cross-sectional area as the others. It will beappreciated that the fluid circuits 2260, 2270, 2280, and 2290 canassume any number of shapes besides the illustrated shape.

However, it will be appreciated that the cross-sectional areas of thefirst, second, third, and fourth fluid circuits 2260, 2270, 2280, 2290may differ from one another depending upon the given application. Forexample, the distance between the second and third annular walls 2220,2230 may be increased relative to the distance between the first andsecond annular walls 2210, 2220 resulting in the third and fourth fluidcircuits 2280, 2290 occupying a greater area than the first and secondfluid circuits 2260, 2270. Alternatively, the distance between thesecond and third annular walls 2220, 2230 may be made reduced comparedto the distance between the first and second annular walls 2210, 2220.This results in the third and fourth fluid circuits 2280, 2290 occupyinga lesser area than the first and second fluid circuits 2260, 2270.

Exemplary uses of the duct 2220 will now be described; however, thefollowing examples are merely exemplary and do not limit the scope ofpotential uses. In a first application, both a first fluid flowing inthe first flow circuit and a second fluid flowing in the second flowcircuit are maintained at nearly equal temperatures and heat exchange isnot an issue. In a first case, both fluids are bi-directional in thatthe first fluid flows up and down in the first flow circuit and thesecond fluid flows up and down in the second flow circuit. Theconfiguration of the first and second flow circuits permits the firstfluid to either travel up or down the first fluid circuit 2260 and thenflow in an opposite direction in the second fluid circuit 2270.Similarly, the second fluid may travel either up or down the third fluidcircuit 2280 and then flow in an opposite direction in the fourth fluidcircuit 2290. When heat transfer is not desired, as in this embodiment,the bi-directional flow capabilities in each of the first and secondflow circuits provides versatile fluid routing for the first and secondfluids. This permits the user to easily and conveniently deliver and/orremove the first and second fluids to or from one location of the duct2200.

In a second case, the first and second fluids are still at nearly equaltemperatures and heat exchange is not an issue. In this second case, oneof the first and second fluids is bi-directional while the other isuni-directional. For example, the first fluid travels up or down thefirst fluid circuit 2260 and then flows in an opposite direction withinthe second fluid circuit 2270. The second fluid flows either up or downeither the third or fourth circuit 2280, 2290. Thus, one of the thirdand fourth circuits 2280, 2290 does not have a fluid flowing in it andtherefore remains unoccupied.

In another embodiment, the duct 2200 is used to transfer the first andsecond fluids having different temperatures. However, heat exchange isundesirable in this embodiment and therefore the first and second fluidsmust be properly located relative to one another. One of the first andsecond fluids flows bi-directionally while the other flowsuni-directionally. For example, the second fluid flows up the fourthfluid circuit 2290 and flows down the third fluid circuit 2280, whilethe first fluid flows either up or down the first fluid circuit 2260. Inthis embodiment, the second fluid circuit 2270 is left unoccupiedbecause heat transfer between the fluids flowing at differenttemperatures within the adjacent second and third fluid circuits 2270,2280 is undesirable. By leaving the second fluid circuit 2270unoccupied, a “buffer” or insulting zone is formed between the first andsecond fluid circuits 2260, 2270. This permits the first and secondfluids to flow within their respective flow circuits without heattransfer occurring between the first and second fluids.

One potential application for this is to have the first fluid be acooling fluid, which flows up the first fluid circuit 2260. The firstfluid circuits 2260 are the circuits which border the first annular wall2210 and therefore it is desirable if the fluid flowing within theoutermost radial section of the duct 2200 has a temperature cool enoughto permit the user to grip, touch, or otherwise manipulate the duct2200. This self-insulating capability protects against having a hotexterior surface that can accidentally be touched and also reduces theamount of heat thrown off the external surface 2211 of the duct 2200 toa person in close proximity. Advantageously, the first fluid is alsodelivered to the upper portion of the duct 2200 where it can be directedto and used in one of the upper components of the Stirling engine (e.g.,a combustion chamber).

In another embodiment, the first and second fluids are at differenttemperatures and heat exchange is desirable between the first and secondfluids. One fluid flows in a bi-directional manner while the other fluidflows in a uni-directional manner. For example, the second fluid travelseither up or down the fourth fluid circuit 2290 and then flows in theopposite direction in the third fluid circuit 2280. The first fluidflows either up or down the second fluid circuit 2270 with the firstfluid circuit 2260 being unoccupied. Because the first and second fluidsare at different temperatures, heat transfer results between adjacentfluid circuits. In other words, the higher temperature fluid flowingeither in the second fluid circuit 2270 or the third fluid circuit 2280will transfer some of its heat to the fluid flowing in the other of thesecond and third fluid circuits 2270, 2280. This configuration permitsfluids to be thermally managed in a system, which provides forbi-directional flow. The fluids can be transferred within the duct 2200from one location to another location in an environment in which heattransfer is permitted or discouraged between the fluids.

Once the flow direction and circuit location of each of the fluids isdetermined, the entry and exit locations for each of the fluids aredetermined. FIG. 33 illustrates various methods of introducing fluidsinto and out of the first and second fluid flow circuits from either aninternal surface 2209 or an external surface 2211 of the duct 2200. Morespecifically, first and second windows 2300, 2310 are formed in theinternal surface 2209 of the duct 2200. The internal surface 2209 isactually an inner surface of the third annular wall 2230. In theillustrated embodiment, the first window 2300 is formed in an upperportion of the third annular wall 2230 and the second window 2310 isformed in a lower portion of the third annular wall 2230. The first andsecond windows 2300, 2310 are illustrated as generally being in axialalignment; however, they do not have to be arranged in such a manner(e.g., they can be formed in a non-axial arrangement). The first andsecond windows 2300, 2310 may assume any number of shapes and sizes solong as each one is in fluid communication with the fourth fluid circuit2290.

The first window 2300 may function as an inlet window receiving thesecond fluid which is to flow within the fourth fluid circuit 2290 or anoutlet window, which receives the second fluid from the fourth fluidcircuit 2290. The second window 2310 will thus function in an oppositemanner compared to the first window 2300 in this embodiment. In otherwords, if the first Window 2300 is an inlet window then the secondwindow 2310 is an outlet window and vice versa.

It will also be appreciated that both the first and second windows 2300,2310 may share a common function in that the first and second windows2300, 2310 may either both function as inlet windows or both function asoutlet windows. In the instance that they both function as inletwindows, the second fluid is introduced into the first and secondwindows 2300, 2310 and then flows within the fourth fluid circuit 2290until it either exits at some location or is directed into the thirdfluid circuit 2280, where is flows in an opposite direction. In theinstance that the first and second windows 2300, 2310 both function asoutlet windows, the second fluid exits through the windows 2300, 2310 asit flows within the fourth fluid circuit 2290 from another location,such as the third fluid circuit 2280.

FIG. 33 also illustrates forming a third window 2340 in the externalsurface 2211 of the duct 2200. The third window 2340 is in directcommunication with the first fluid circuit 2260 and functions as eitheran inlet window or an outlet window for the first fluid. Both the firstand second fluids are typically pumped or otherwise directed through thefirst and second fluid circuits 2260, 2270 of the duct 2200 from onelocation to another location.

FIG. 34 illustrates another aspect of the duct 2200 and morespecifically, FIG. 34 illustrates particular ways to introduce one ormore of the first and second fluids into or out of the first and secondflow circuits from either end of the duct 2200. The duct 2200 willusually have end plates, generally indicated at 2299 at one or both ofits ends. The end plates 2299 may be constructed so that selected onesof the first, second, third and fourth circuits 2260, 2270, 2280, 2290are open while selected ones are sealed. The circuits that are openserve to either receive or discharge the respective fluid flowing. Inthe exemplary embodiment shown in FIG. 34, only the circuits that areopen are illustrated. For example, the illustrated first and secondfluid circuits 2260, 2270 are formed such that the open circuits areoffset from one another. However and as illustrated by the third andfourth fluid circuits 2280, 2290, opposing third and fourth fluidcircuits 2280, 2290 may be open. The illustrated embodiment shows a setof third fluid circuits 2280 that are open across from a set of openfourth fluid circuits 2290. Furthermore, another set of open third fluidcircuits 2280 are shown as not having any open fourth fluid circuits2290 facing them.

The entry and exiting manifolding for two bi-directional fluids is lesscomplex if either the entry or exit manifold (e.g., window) for abi-directional second fluid has its fourth fluid circuit 2290 manifoldformed in the internal surface 2209 of the duct 2200, as shown in FIG.33, while a bi-directional first fluid has its first fluid circuit 2260manifold on the external surface 2211. Accordingly, the manifolds forthe second and third fluid circuits 2270, 2280 are most readily locatedon one or more of the end plates 2299 (as demonstrated in FIG. 34). Inthe instance where the first fluid flow uni-directionally, the circuitmanifold may be located either in one or more end plates 2299 or it maybe formed in the external surface 2211 of the duct 2200. One of the morecomplex embodiments is where both the first and second fluids flowbi-directional and both the entry and exit manifolds for both the firstand second fluids are formed in the same end plate 2299. Even in thisembodiment, the manifolds may be formed to permit such entry and exitingof both fluids at the same end plate 2299.

FIGS. 35 and 36 illustrate yet another aspect of the present Stirlingengine assembly. FIG. 35 is a partially exploded perspective view of ahighly efficient heat exchanger, generally indicated at 2400. This typeof heat exchanger 2400 is usually referred to as a pre-heater. Such apre-heater is used to transfer wasted heat from exhaust products toincoming feed fluids. This enhances the economic efficiency of manyenergy conversion or chemical processes. High thermal efficiencies ofthese heat exchangers are characterized by (1) large surface areasbetween the two fluid streams, (2) thin and highly conductive materialsseparating the two streams, (3) low pressure drops, (4) uniform massdistributions between the two streams for uniform heat transfer, and (5)long residence times. If feed flexibility allows, counter flow heatexchangers are more efficient than parallel flow devices.

For low capacity units, tubular heat exchangers are typically used. Onefluid is passed through the inside of the tube while the other fluid ispassed over its external surface. The tubes can either be coiled in atransverse plane with the other fluid, e.g., gas, crossing it axially,or a series of parallel longitudinal tubes can be arranged axially withthe opposite fluid either passed axially or crosswise through the forestof tubes. For high mass throughput heat exchangers, tubular designsbecome less efficient. This may be due to having to use fewer thanoptimum large diameter tubes or having to use less tubes to limitpressure drops. These types of heat exchangers also incur highmanufacturing costs for large numbers of small diameter tubes with lowvelocities to limit the pressure drop where large component envelope isrequired.

One approach for designing high mass throughput heat exchangers whichovercome the above-noted limitations is to use pre-formed thin sheetstock, generally indicated at 2410, with side by side planes of oppositefluids in adjacent gaps. This improved design offers the benefits of (1)large surface area, (2) low pressure drop, (3) uniform massdistribution, (4) small fluid hydraulic diameter and (5) lowmanufacturing cost. The pre-formed stock 2410 is bent to assume agenerally serpentine shape. This arrangement results in first fluid flowpaths 2430 being formed to carry the first fluid as well as second fluidflow paths 2440 being formed to carry a second fluid. The first andsecond fluid flow paths 2430, 2440 are formed in an alternating patternsuch that the first and second fluid flow paths 2430, 2440 are adjacentone another to permit heat transfer between the first and second fluidsas they flow through the heat exchanger 2400.

The biggest challenge is the lowest cost method of blocking two ends2431, 2441 of the pre-formed stock 2410 so as to form a fullyoperational, efficient heat exchanger. FIGS. 35 and 36 show one method,whereby two end plates 2450, 2460 are used. The end plates 2450, 2460include inlet and outlet distribution feed systems for transferring anddirecting the fluids into the first and second fluid flow paths 2430,2440.

FIG. 36 illustrates an effective yet low cost method of attaching thepre-formed stock 2410 to the end plates 2450, 2460. FIG. 36 is across-sectional view of a section of one of the end plates 2450, 2460.Retention channels 2470 are formed in a first surface 2459 of each ofthe end plates 2450, 2460 using any number of suitable techniques, whichpermit channels of precise dimensions to be formed in a substrate, suchas end plates 2450, 2460. For example, suitable techniques for formingthe retention channels 2470 include but are not limited to an endmilling process, photo etching or other means for forming carefullytailored channels within the end plates 2450, 2460.

The retention channels 2470 are formed and spaced in a pattern, which iscomplementary to the dimensions and shape of the pre-formed stock 2410.This permits ends 2430, 2440 of the pre-formed stock 2410 to be easilyaligned with and inserted into the retention channels 2470.

Braze material 2480 is packed into each of the retention channels 2470to provide a material to bond the preformed stock 2410 to the end plates2450, 2460. The braze material 2480 may be introduced into the retentionchannels 2470 in a number of different forms. For example, the brazematerial 2480 can be packed into the retention channels 2470 via foil,powder or slurry mixtures. The braze material 2480 is then exposed to asuitable treatment process to cause the bonding between the pre-formedstock 2410 and the end plates 2450, 2460. Typically the braze material2480 is introduced to heat via an oven or other heating device and thisheat causes the braze material 2480 to melt and flow and its re-coolingprovides the bonding between the pre-formed stock 2410 and the endplates 2450, 2460.

The formation of retention channels 2470 and the use of braze material2480 provide an effective and low cost method of sealing the ends 2431,2441 of the pre-formed stock 2410. As the braze material is heated itflows around the surrounding components (the pre-formed stock 2410 andone of the end plates 2450, 2460) and creates a bond betweentherebetween when the heat is removed and it re-cools and hardens.

In another aspect, the end plates 2450, 2460 are attached to thepre-formed stock 2410 in two discrete processing steps. Morespecifically, two braze materials 2480 are used with one braze material2480 having a sufficiently higher melting point than the other brazematerial 2480. In this embodiment, a first braze material is disposed inthe retention channels 2470 of one of the end plates, for example endplate 2450, and then the pre-formed stock 2410 is inserted into theretention channels 2470. The end plate 2450 and at least thecorresponding end of the pre-formed stock 2410 is placed into a heateror the like and is exposed to temperatures equal to or greater than themelting point of the first braze material. This results in the meltingof the first braze material and the subsequent bonding between thepre-formed stock 2410 and the end plate 2450 upon re-cooling.

Once the end plate 2450 is securely attached to the one end of thepre-formed stock 2410, a second braze material is disposed in retentionchannels 2470 formed in the other end plate (in this case end plate2460). The second braze material must have a melting point temperaturesufficiently lower than the melting point temperature of the first brazematerial because typically, the complete heat exchanger 2400 will beplaced into the heater (e.g., oven) and therefore the hardened firstbraze material is exposed to heat again. The heat exchanger 2400,including the end plate 2460 with the second braze material, is exposedto temperatures equal to or greater than the melting point temperatureof the second braze material but less than the melting point temperatureof the first braze material. Because the temperature of the heater isnot permitted to reach the melting point temperature of the first brazematerial, the first braze material does not re-melt but instead is leftintact.

When each of the end plates 2450, 2460 is attached to the pre-formedstock 2410, the respective end plate 2450, 2460 is preferably disposedduring the heating operation so that the retention channels 2470 openupward so that the braze material 2480 will not flow down the sides ofthe pre-formed stock 2410. If the end plate 2450, 2460 is positionedoppositely in the heater, the braze material would have a tendency toflow by gravity down the sides of the pre-formed stock 2410 as soon asthe braze material reaches its melting temperature. This is undesirablebecause it results in the braze material flowing out of the retentionchannels 2470, thereby increasing the likelihood that a weak bond willresult between the pre-formed stock 2410 and the end plate 2450, 2460.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to the embodiments described thus far withreference to the accompanying drawing. Rather the present invention islimited only by the following claims.

1. (canceled) 2- A multiple cylinder Stirling engine, comprising, incombination: a plurality of individual closed-loop hot ends, eachdistinct from the other, wherein a single said individual closed-loophot end is associated with a single cylinder of said multiple cylinderStirling engine, and wherein each said individual closed-loop hot endincludes a plurality of heat sources. 3- The multiple cylinder Stirlingengine of claim 2 wherein each said individual closed-loop hot endfurther includes a heat transfer system. 4- The multiple cylinderStirling engine of claim 2 wherein each of said plurality of individualclosed-loop hot ends is a platelet hot end.